Exp'd with gastank sealer?

I need to build or have built a diesel tank for my Espar heater. It's gonna be a bit tricky as I need it to slide under the bus and latch in place, then slide out for refilling. I'm thinking of just buying some thin-wall tubing and welding the sucker up just the way I want it then sealing it with that Por-whatever tank sealer. It's only gonna be about two gallons capacity. Is this a reasonable use of the product? Is it overkill on my part? Will it cost me more than it's worth - can have a custom stainless tank built for around $150. TIA - Dave