Without reading about it, I made a wooden frame as wrk101 suggested. I used hinges I had laying in a box for 20 years so I could "fold up" the frame for storage and it allows me to adjust the clearance around the bike frame. I cut twice and it is always too short! The plastic sheets I had had holes, so I wasted about 5 gals. In my youth, I cut trees in eastern Oregon and have the hard hat from those days. I used it to raise the plastic sheet inside the major tubes to reduce the amount of acid solution.

I think supporting contact with the tubes should be avoided to allow the acid to "circulate" around the tubes, so as appealing as the peanut idea is, I would rather waste the acid. It is really dilute anyway and is not like hydrocloric acid!

BTW: Use 2x8 to be able to get the depth for the rear DO spacing.