Why not make a raised garden in an old bath tub? The reason I ask is that when my hubby and I were at a flea market, they had a very large old bath tub for sale. I said to him, that will make a very good raised bed garden; just put some holes in the bottom. Then fill the bottom with rocks or something, so it will take less dirt to fill it up with composted manure.
You'll have a raised bed garden for life and for somebody else after you have gone on to a better place. I already have the above with cement blocks around it. It will also last longer than I will. Good luck.