It will not affect it to cut the solar cover. It is made up of a series of individually sealed bubbles. If you cut one bubble the rest remained sealed. Just like packing material.
It will not need to be trimmed out on the cut edge unless you just want to use trim to hold it in place against the greenhouse frame. Which is a good idea.
I think you will almost pay for the solar cover the first winter in what you save on propane.
I switched from propane to electric space heaters and the cost for the whole winter was what propane was for 6 weeks. I also lowered the temperature to around 45-47.

Thanks, Cactus.

I thought I might somehow tack down that north end around the door and on the sides, that might keep the cold air from blowing in between the GH and the pool cover. Do you cover the ends of your GH, or just the top? Did it reduce the condensation on the inside of the glass?

I covered just the north wall and a little down on each side wall. That was the largest cover I could get without paying freight charges. I put a layer of regular plastic inside on one sidewall that rans NorthEast. And I had already put a layer of plastic inside on the back North wall before I bought another solar cover for it.
Yes, it did reduce the condensation. I don't remember having any at all on the ceiling. Just the front wall that was not covered.
Look at 'My Page' to see how far the cover came down on the sides.
The wind was a problem esp. in March. So it's a good idea to seal it tight so air doesn't get under it.
I finally just took some very heavy rope and threw it over the ends and tied it down so wind couldn't get under it.

Hi Cactus;

Where did you get your solar pool cover from?

Dave

Sorry, another stupid question I had not thought to ask at the beginning...what about ventilation? The cover as I envision it would cover up my ridge vent. The ridge vent is the only one I leave functional in the winter.

Last winter I covered the intake louvers and exhaust fan with styrofoam insulation. They are pretty drafty and I would hate to have to leave them uncovered.

I suppose I could just crack open the glass on the screen door as needed.

I bought the two 20x40's from Amerimerc. And the 16x32 from America's Best Pool Supply.
Do a comparison and see which one comes out better with the shipping charges.
America's Best has the lowest price (98.99) but the shipping maybe higher than Coolpooldeals.com (99.95). Amerimerc (124.75) but shipping is free. All these prices are for a 16x32.
Be sure you get Magni-Clear not BLUE or the thinner 12mil.
And get the inground cover. The above ground are oval or round. You want a rectangle for better fit.
Sometimes the descriptions are confusing to read.
Do a search and you may even find a better deal.