The fuel tank for the WW2 jeep is under the driver’s seat as pictured below. It’s not the most comforting thing about driving a jeep but I guess you get use to it.
a. Description. The fuel tank pictured above is the “late” version with the wide mouth opening. The ”early” version had a narrow mouth and did not have a filler extension. Both versions were located under the driver’s seat. An extension filler neck on the “late” version can be pulled up to facilitate filling the tank from a container. After removing the filler cap, pull up on the filler extension, and turn to the right to lock it in place. To remove the filler extension from the tank turn it to the left and pull up.
b. Removal. Drain fuel by removing drain plug in left side of tank. Remove bolts in seat rear flange and front legs, then lift out seat. Remove filler cap. Disconnect fuel gage wire and remove fuel gage unit by taking out five screws. Disconnect fuel line from tank, under vehicle. Remove bolt holding tank to wheel housing, remove bolts in tank straps, and lift out tank.
c. Installation. Clean out fuel tank sump in body, and install tank in place. Attach tank straps and bolts, also bolt holding tank to wheel housing. Connect fuel line to tank. Install fuel gage in tank, and attach wire to gage. Set seat in position and secure in place with bolts in front legs and seat flange. Fill tank, install cap and check tank and connections for leaks.
From TM 9-803.
While not shown above, there is also a narrow mouth fuel tank that was on early WW2 MBs/GPWs. Good reproductions of the fuel tank are available today. You can find both versions even on Amazon.com (as I write this anyway): Omix-Ada 17720.02 Wide Mouth Fuel Tank and the Omix-Ada 17720.01 Narrow Mouth Fuel Tank. The narrow mouth fuel tank is for early jeeps to around early 1942. The wide mouth tank is for all others.