Most new and older carts are both too light duty for me. They are OK, but not worth a lot of fuss to keep them looking good. . I don't think this can appreciable extend its life. . On my old cart, paint and lack of rust had little to do with its failings. It was more about stress fractures around bolt heads, axle fatigue, tire rot, weld cracking than finish. Just got to the point where my money and time were best directed at a better solution. My neighbor's old cart is about 30 years old, left outside all the time. He's never painted it. It's not pretty, but still goes for him. But, it too is showing signs of metal fatigue.
What is lacking on the market is something more robust, along the lines of the Country Manufacturing Inc. carts, only better designed, with a couple of dump options (like electric and hydraulic remote dump). There just isn't much to choose from at heavier duty than the 10/17 cu. ft models sold today, unless ready to spend $1500 or more. I finally gave in and bought one of those CMI carts and then modified it to be what I want. It still could use a heavier hitch, and benefit from steel sides/bottom. But, it works pretty good. For about $500 I got a 1 ton cart with hydraulic dump that hooks up to any 1/2" set of remote ports. To me, I'd rather put my efforts into this approach where I get a much superior cart.
Of course if I had an old cart around and it met my needs, I'd probably just use it til it died. But, I doubt I'd spend one nickle or any time treating the finish.
I suppose the sheet would protect the paint and the thin stuff should be lightweight.
