Vinyl decals will fade and age with time if it is cheap vinyl. You can buy it in different grades and from different manufactuers (avery,oracal,3m,lg, and more). You can get most of them in a 4 year, 6year, 9year outdoor vinyl. If you use something good like a 9 year vinyl it should last on you tank for a long time since it will not be abused by the weather as an outdoor sign would. Also some vinyls are made for surfaces with curves and some are made for flat surfaces.