Lew might have been more helpful in his answer.

Vinylester resin is preferred for fuel tanks because most fuel tanks
hold gasoline - gasoline is incompatible with most (but not all) epoxy
resins. Your tanks are diesel so you probably could use epoxy - except
that diesel is increasingly laced with alcohol and even ethanol which
is usually not compatible with epoxy.

Below is a link to some instructions from West - while they say you can
use West epoxy they sure don't sound enthusiastic. They also note that
fuel tanks are heavily regulated by federal law. While you can build
your own tank, if you want to sell the boat (at least in the US) you
might have an interesting legal exposure. You also may have challenges
obtaining insurance on the boat if you admit to the homebuilt tank.

http://www.westsystem.com/ewmag/18/pdf/tanks.pdf

If you do go ahead - as others have suggested use a layer or two of
cloth. Also, if the tank is over 20 gallons or so, don't forget
baffles.

Carl