I bought a Gladiator 3" square-stock steel workbench frame, 62" X 22" & it's being set-up to store a couple of Honda CB77 vintage motorcycles. My preliminary thought is to use a 3/4" piece of plywood sheet, ripped lengthwise, doubled-up, so that's 1-1/2" thick, glued & screwed. I don't think I really-need eight feet, I'm thinking of cutting it to seven feet in-length.
I bought the frame off craigslist, one of the screw-out steel & nylon adjustable feet was frozen. he also didn't include any fasteners, so I used that to drop the price by 20%, done-deal. Luckily, I'd recently-purchased a set of Cornwell bolt extractors
http://corporate.cornwelltools.com/webcat/products/AE5SCST-%2d-5-Piece-Screw-Extractor-Set.html# and this was my first use of them. They worked perfectly. I drilled a~3/16" X 1/2" hole in the metal screw, drove-in the #2 extractor, and the screw backed out, perfectly. I had 'shocked' the pin with a drift punch and PB Blaster, I would have used some heat, but the 'foot' has a poly plastic wide round disc inside the 3" square workbench leg. No pics of the work, but now that all four of the screw-out floor-height adjusters are functional, I can do the workbench top, throw a set of eyelets at the ends for four tie-downs to hold the upper bike stationary, and gain some floor-space where one bike was.