look at our raised bed format, it will work in your situation, maybe a pic or 2 of the large trees might help to i'd them for you?

remember the larger the worm farms the more bio mass you need to feed them with, collecting scraps from neighbours is a good diea, we have a pic of our homemade worm farm when we had on, made it from a 1/2 44 gallon plastic drum.

for us our worm farming along with composting happens in the garden beds now right where all their benefits are needed.

anyhow check out our garden pics might be some ideas there for you?

len

"and after the first or second crop I am back to having very poor soil. As if the goodness is leached out over a short period of time. "

over time compost and mulches break down and reduce to almost nothing which is where the compost is disappearing to, you need to add more compost each season and also cover crops are another way of adding organics if the area is not being used year round. Its not a matter of doing it once - you also have to keep up with it as long as you are using the area to grow vegies.