You want specifics? Ok, 16 gage sheet steel, a gasketed top opening
12"x16" on a piano hinge, spring loaded pins to hold the lid closed, the
box sealed to the floor, and vented through the floor with a simple drain
hole, roll some beads in it so it won't "drum', and paint it to match the
interior. make it big enough to enclose the pumps also. Run the the fuel
lines through the case with gommets or bulkhead fittings. Cut the center
out of a baking pan and mount it to the fill-plate flange so you can
easily mop up spilled fuel from re-fueling.

I'm sure many of you could come up with a lighter, better set-up than I
have just described, You could build it from aluminum, incorporate the
structual retention into the "liquid proof case", so it's lighter, or
just build a sealed case with a tower / cover on it in place of the ATL
container (as Lurch has done) and those would be acceptable also, if you
have specific questions or an example, contact me via R-A forums and I'll
give you an answer, but asking me to design it for you is ???

.... yeah whatever, "dude"