I agree the support structure for a bag system would seem to be a key ingredient. As we saw in many earlier posts often times this supporting strength fails in plastic bins where large areas of the support wall is cut away for the collection bin.

"hang it on the stand" A strong stand, right?

A catch basin for any wayward drips underneath might be appreciated.

I do not see a problem with the bag being not breathable due to waterproofing. It would be the same as a plastic sided bin.

To sew the bottom cinch maybe use fishing line or other plastic not cotton thread. Maybe skip sewing and just cinch it off with a cord on the outside.

Remember. Bedding is your friend. It will make wet foodstuff less wet and hold moisture at the center of the system to keep the worms alive for when the system is left to dry out. Anything that drips out add back in on top along with some dry egg carton, or coffee tray or corrigated cardboard material.

To continue with the money saving, low earth impact theme, you may find worms for free in friends compost heaps.

Maybe somebody can correct me if I am wrong but if a worm is found in the top half of a compost heap is it probably a compost worm? If you are lucky you will find them clustering around a particulary tasty bit of rotting food. Tear apart the compost heap with a three prong claw hand tool. Have a bucket or back pack ready to put your new little buddies in. Grab some of the happy material they are in too.

Many peoples first attempts do not work. Mine did not. But their second attempts do work. Thus the huge advantage of starting on a shoe string budget. You may save even the cost of the "pound of worms" if your crew is fruitful and multiplys.

pkon that's a clever idea. Since another opening is needed for harvesting I'd be tempted to turn it upside down to use the existing zippered opening for that and cut a hole it the pack's bottom (now it's top) for feeding. That way harvesting would use a zippered opening that is probably stronger and better constructed than anything I could sew. There would also be some drainage through the zipper.

For more ventilation multiple needle holes could be poked in the sides of the pack.

boreal_wormer, thanks so much for the "upside down" idea. I will take a close look at this. a neat thing with this idea is that the bottom of the backpack is bigger than the top, and so putting it upside down would give that "narrower at the bottom" tapered effect that the nice worm bags have. another advantage would be that as you point out, the zipper is super strong, and so it'd hold no problem. I need to confirm that the drainage through the zipper is sufficient--I'm guessing it is.

One thing I'd need to figure out is how to make it so that the newly created top opening could be easily opened and closed. one idea would be to make the hole in the bottom, and then sew a "no see-um mesh" type material around the backpack in a loop, with enough material on the free end of the mesh to attach a drawstring. so it might look like this from the side, m being mesh, d being drawstring, b being backpack.

mmmmmmmm
dddddddddddd
mmmmmmmm
mmmmmmmm
mmmmmmmm
bbbbbbbb
bbbbbbbb
bbbbbbbb
bbbbbbbb
bbbbbbbb
bbbbbbbb
bbbbbbb
bbbbbb
bbbb

Feedback or alternative ideas welcome from all.

equinox, thanks for your reassurance on the bag. I just don't want to do anything *obviously* dumb, you know? I think I will give this a go based on your comments.

in terms of the stand, I'm thinking I'll do the same as with the fancy worm inn that I bought, and use 3/4" PVC. It's held up nicely for me so far. I could go with 1" PVC but it seems unnecessary. I can get the 3/4" PVC pipe at home depot for $4 (I think that's for 2x10 foot pieces)

For the corner pieces I can order them from dpsbargainbasement.com for .87 each plus shipping. Then even have 4-way pieces if you want to have several bins connected to one another, which I'm going to try--should arrive in the mail this week. (in that way I can add an extra stand with only 4 more connector pieces, as opposed to 8 for the first one.) shipping costs suck (not their fault) but it's the kind of thing that if a group of people in the same area wanted to buy, then the numbers start looking nice. the bulk discounts don't hurt either...

Here is a link that might be useful: PVC Connectors at a good price

As equinox mentioned, while not a problem in itself the waterproofing might make it act more like a bin than an inn. Just something to keep in mind in case you've watched those inn feeding videos where food is dumped in en masse :). So you will get the flow through aspect and the easier harvesting from the bottom, might be different on the aeration and processing capabilities.

One thing with the zipper might be closing it again. With the Inn (hard to see until it's used) the bottom opening is made with material that's looser/larger than the canvas material around it. So when the system is loaded and heavy the canvas might be pulled tight, but the drawstring opening at the bottom is always loose which makes it easy to close.

Once your VC settles and if it tends to drop while harvesting, you might find it hard to zip it again if the weight is pulling the zipper appart. Like trying to zip shut a stuffed suitcase. In this case you'd have to squeeze or push stuff back up intead of sitting on it to close it ;). Just something to keep an eye on.

Good luck :)

Sewing might not be necessary. I cover my bin with a square piece of sheer curtain. The curtain drapes down a foot on all sides. Nothing closes it 100%. For some reason fruit flys do not fly down to escape. It is see through. If there are flys waiting to get out I can just wait to add food until they are gone. Water can also be poured through without removing the cover.

I like this idea and will steal parts for my next bin.

Go read a thread named "5 gallon bucket x worm inn - call it a F1 hybrid". This shows a bag style bin I built with nylon and a 5 gallon bucket. While there is a significant difference between the backpack and my hybrid the volume is about the same. I have been fighting this bucket bin drying out for the last two months but the much larger worm inn next to it chugs along fine. My thinking is the surface area is so great relative to the mass that it drys out annoyingly fast.

Here's my idea if you have a sewing machine.

Take 2 backpacks and slice up the bottom of both of them. Sew both of them together such that they are bottom to bottom. This way you end up with a larger mass to hold moisture but will drain excess and you will have a zipper opening both for feeding and harvesting.

Thanks all for your ideas and encouragement. Your input was the inspiration for the next step in this idea.

So I was at goodwill looking for cheaper, unlined backpacks and I came across a cheap, unlined gym bag.

Now think about it: it's got strong handles, zippers on both ends, breathable material. Perfect!

I'll do the stand from home depot PVC, and use the corner pieces from the place I mentioned above.

The one thing will be securing it the stand from the handles so that it hangs vertically rather than diagonally. I'll post a picture when I get it set up.

Here are the pictures, pre-setup.same link is below, too:
http://www.flickr.com/photos/77024342@N04/sets/72157629393150769/

Was able to hang it for now from my existing stand. Can easily add another stand when needed.

For drainage, I'm thinking of pocking holes in the inner liner towards the bottom. Drainage water would then go to the bottom zippered compartment, and could be released from there. But I wonder how big the holes need to be, and how many of them and where, to get proper drainage.

For feeding, I need to decide if I do that from the side zipper, or from the top compartment.

If from the top compartment, then I need to cut out the inner liner between the top zippered part and the main compartment.

This bag has a cheaper inner construction than the backpack I picked up, so it'll be more breathable. I think in terms of breathability, this one will be on par if not better than the fancy worm bags.

Any opinions or other advice?

Here is a link that might be useful: pre-setup worm bag from gym bag pictures

You may need a plan "B" for the zippered harvest area. I suspect the castings will quickly leave the zipper useless. Some kind of drawstring modification may be required to avoid dump and sort harvest I would remove the inner dividers and NEVER open the side zipper. Feed thru the top zipper.
Good luck, I love the concept. Keep us posted.

I agree with the others about not using the zipper on the bottom. I would be afraid it would rust solid in no time.