One issue may be having a currently certified tank is a requirement of the filling stations. I think certifications were typically marked on the tank some how. It wasn’t an issue when tanks were just exchanged. I’ll probably look for a source for a new tank.I'm interested to hear of your findings. I'm in the purchase process of a boat with CNG tanks and I'm not all that familiar with CNG. I do have a CNG fill station (for cars and trucks) near me so I'm exploring the adapter route.