What seems to happen is that heat removes the rust resistance of the various grades of steel. High carbon content steel is pretty good until it's heated and then the rust speeds up. Stainless steel rusts too but so slowly it about never becomes a problem again.
In decades of battle with this problem I find a couple things that work well:
1. Regular or high temp (that anti-seize aluminum type) grease just plain stops the progression but is ugly to look at and attracts dirt. For an antique or classic car you probably don't want that. You can get spray grease and I use that like crazy when I get a car that I intend to keep for 10 or more years which is most of the vehicles in my own corral. I'm beyond bad and don't like vehicles newer than 1989 and once said I'd never own anything newer than 1979 but clearly I lost the battle and now will consider up to 1999 but that's it for a while.
2. Keeping heat away will help slow rust down but you have to start with no rust. Rust is like a virus that must be killed or it starts right up again. There are effective rust killers that rely on the rust to make the product work. Now sold everywhere it seems and a bit expensive. It contains barium and reacts with the rust and turns black which is then a primer. It must be applied and let dry without any moisture or it's a waste. You can't even reuse a container or brush or it quits. I use this and then coat parts with common BBQ semi-flat paint which looks factory on many under car hidden spots. It tolerate the heat and more importantly continues to keep air and moisture away from the metal giving you the best shot at appearance and rust protection and even it will give up but then easier to redo if you have a car long enough as I do.
If you wrap something keep in mind you might be trapping in moisture which could then be counter productive,
T
Tom Greenleaf - MetroWest Boston - USA
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