Even if you put several coats of clear over the murals and handle them carefully others won't, like the guys doing the fills, VIPs, Hydros, and some boat operators so they will get scratched. Then how do you get it off without heat or tank damage?
Also, some shops like South Shore Divers wont fill a tank with anything other than factory paint. By the way, they have one tank in the shop that was stripped with heat, painted and burst during a hydro that they insisted on before they would fill it.
You can put murals on the tanks but it will cause more aggravation than its worth.
There are wrap around stickers with art on them that will cover most of a tank and if they get torn up you can get them off with some solvent.
I would suggest that you just leave them the way they are.
TT