8 feet by 40 feet? You can place wide boards across the width which would divide it into several smaller blocks that can be worked from 3 sides. Place them so that the divisions allow you to reach the middle of the section from all 3 sides The boards will disperse your weight so that walking on them will not cause as much compression. Clay isn't a bad thing actually. It holds water and nutrients quite well, but just needs a little help. This could potentially be a really great garden. If you can incorporate a lot of peat moss or coconut coir, it will improve the tilth of the soil immediately and permanently. After that, all you would need to do is keep it well mulched and you'd have some great soil that would need a lot less supplemental water. If I were in this situation I would set up some additional beds (if there's room) to take up the excess 'topsoil' so you can add plenty of peat moss. It will be hard to mix peat moss all the way down to the bottom in that main bed so I would mix in as much as I could in the top section, install some WORM TOWERS then add some composting worms as well as some nightcrawler type worms that will burrow deeply and help build up the lower levels and improve the drainage. Keep the worm tubes fed with organic matter. (Worm tube instructions at link below) I would then plant a mix of deep-rooting cover crops (comfrey, alfalfa, clover, or whatever would work for this season and start growing now in your climate) which will root deeply and add organic material to those lower levels. Cut them down just before they begin to flower, and leave it all there on top as mulch. If necessary, spread it out a bit to let it dry some first, and chop it up a bit if you feel so inclined. Keep the bed mulched at all times. By next spring I think you'd have a great, very fertile bed ready for planting. Just open up holes in the thick mulch and put your seeds or plants in the soil. Leave the openings in the mulch to let the plants grow. Along the back, plan to plant things that you can train up the fence (melons, cukes, beans, tomatoes, etc. If parts of the plant are allowed to grow out the other side, you can harvest from there. Large fruits will need support as they grow which can be done by making little hammocks from pantyhose tied to the fence. Please keep us posted on how things go! Here is a link that might be useful: Build a Worm Tower

I cut the 2x4 in to the desire length, stack them up on both side of the seed trays and place the light corsswise, starting low (maybe 3) add more to increase the high as the seedlings get taller. 2x4 is rather inexpensive from HomeDepot. Hope this help..Happy seeding...

Last weekend after working my butt off all day finishing the second vegetable bed, buying a bunch of cement blocks for the back third planter and transporting them down the hill to the back yard, and hauling 15 loads of dirt down to the backyard. I tried to move the large bed and one leg slipped onto the grass. As I pushed, all the weight tore the wheels and recently added middle legs off. To say I was devastated was an understatement. I had spent a lot of money and the past 3 weekends trying to build something that would last a long time. Today I stopped pouting and fixed it using a car jack and car wheel dollies to push it off the grass to its final place. It no longer has wheels but now it is in the correct position and has plants in it.

My experience (long ago) with "bagged topsoil" is that it is mostly cr*p. The Scotts name might, however, assure some quality. "So called" topsoil is likely to be an accurate description. I agree that you need to just mix compost into the topsoil you already have. I don't think peat moss will really serve any purpose, unless you're trying to lighten up clay. It's pretty pricey as well.