sheet metal may be a pain in the butt ot use as a wrack. for the frame and rails it would be better. with the tubs hanging off the rails.
the problems i see with metal shelving, unless it is really worked, is sharp edges, tendency to bend or dent, if not really heavy gauged. also, overall weight may be alot with stainless steel. heat conductivity and possible electrical current conductivity can be a problem. electricity can be dealth with easily enough, making sure no bare wires touch the metal etc. rusting i don't think is a problem with pure stainless steel, hwoever i am sure you can buy a sort of oil for stainless steel countertops that may not be harmful to snakes, which will protect it from water and scruffing. vegetiable oil could be used and having excess wiped off with teh same effect, and no harm for your animals.
since you know somebody who works with steel as a living, if he can use the tools at work, it should eliminate alot of the work with crimping, shaping etc the steel into the shapes you need for the rack.
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PHLdyPayne