At some point the regulations changed and you can't have a filler inside the vehicle. No idea when this came into play but your modification would have course been carried out 'in period'......
Standard underseat filler on a Series I but Series II onwards was external. My Dormobile has the standard rear tank for a wagon plus someone has added a tank under the drivers seat. The extra tank has a Series I filler neck welded in. It uses a changeover tap from a military IIa.
My Series I has a tank under the back as well as the standard tank and uses two electric pumps and a changeover switch. As you changeover it also connects the sender for the tank being used to the fuel gauge (original owner must have used an identical sender in the additional tank that was added).
Homestar's suggestion of a standard external filler point on the passenger side seems a better idea (like the Military Series II's & IIa's). You may have to cut the rubber filler hose in half add a piece of rigid tube. Partly to allow the different angle needed and also if you're using a standard underseat tank the filler is offset to one side so the filler hose may not be long enough.
Colin
'56 Series 1 with homemade welder
'65 Series IIa Dormobile
'70 SIIa GS
'76 SIII 88" (Isuzu C240)
'81 SIII FFR
'95 Defender Tanami
Motorcycles :-
Vincent Rapide, Panther M100, Norton BIG4, Electra & Navigator, Matchless G80C, Suzuki SV650
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