DEFCON,
More than likely the solvents in the reducers for thinning lacquer or enamels will soak through the cloth and attack the adhesives on the tape. Also lacquer type solvents might attack the plastics used for the fenders on ATVs. It will not be fun getting the mess off. As far as a varnish you would probably have the same problems and the UV protection is not that good and would start flaking off in a short time unless you keep it garaged or covered. Spar varnish like the type used on wood trim on boats would be more weather resistant but usually needs to be redone every year or so. You probably have better luck with a Camo Clad type product. It is sold in kit form and comes in various size sheets.
BoomSplat