If you are filling via the lid a 400lts upright tank is a little tricky as the lid is above door level so you would have to maneuverer a pipe sort of up and over tank to reach filler.
he’s gone and bought one with sliding doors so this might be an issue !
It is possible to fill via the side door and lid you would just have to twist the nozzle sideways then slide it between the door opening and the top of the tank. Once its past the door opening it's fine. My ro/di is in the van so I don't fill via the lid. As the bulkhead slopes to allow seats to be slightly reclined when the tank is in there is a gap at the bottom of bulkhead so my gutter poles (in bag) do slide in if they are stacked. My tank has a 25mm gap at the front between it and bulkhead. I have seen spreader plates under floor but I think you might need to lower the fuel tank or have very slim hands to get the rear frame bolts and spreader plates in on drivers side. I don't know about the front bolts or even if there is a false floor below bulkhead for the 'car version'.
I'm not sure what the dimension is between rear doors and bulkhead as mine had a hole through for poles. I used downpipe and made them long enough to go all the way into the above sun visor storage area leaving enough head room for me at 5'10 to sit in passenger seat probably a bit more headroom.
You can just fit through floor rollers (grippa) and keep the spare wheel in position by bending the carrier about 25mm towards drivers side.
