I think you should have a tank made. I get mine made locally for $10 a gallon. Remove the stock tank and make it fit so that you have lost of capacity and can still fit 8 cubes of grease in the trunk for long trips. You will have to run coolant to your new tank, a nominal expense. Just bundle the coolant and fuel hose together maybe with insulation if you think it is needed.

You stock tank is probably growing polly right now. So it is really a good time and a good idea to put a real tank in. The long trip will pay for the moey and effort.

Good Luck. If you want me to be more detailed just ask.

PS I do not think Vegitherms are worth the money or effort. Sorry Plant drive. A good FPHE is the way to go.