My first try would be to have your 2 main tanks feeding a header tank near the engine. You might be able to use muffler pressure to provide adequate flow to the header tank from the main tanks. One of my concerns would be venting excess pressure from the header tank without leaking fuel all over the place. Maye some sort of check valve would work. You could always use a pump with a fuel level sensor in the header, but that would of course add even more weight an complexity. Good luck!!

Don