If you can find a company who will do it, then Flouride treat the tanks on the inside before use and that will prevent the vapor getting into the plastic, its not the paint or decals thats the problem it is the fuel vapor getting into the plastic. that would probably also allow the tanks to be repaired if damaged as the only reason you cant is that once the fuel vapor gets into the plastic no method of resealing them will work.
However its finding someone who can and will do it for you, there is the problem !!!
The original tanks and other makers such as the Touratech GS tank and the HPN tank now use polymide nylon plastic, and that is impervious to the fuel vapor.