I've just started to kit my P38 out and decided to remove the single seat in the back and use the seat mounting points to bolt my Waeco fridge in...
This also made it easy to run the powerful cable down the left hand side of the vehicle to the split charge fusebox at the front.
I won't be transporting 5 people abroad (3 max) so losing a seat wasn't an issue!
I think you'll want to see Jacob's setup (the guy who has upgraded his EAS to the maximum).
He's done a set of drawers that keeps access to spare wheel well.
I may go this way too. Kinda like Rhino Rack drawers system.
I use my spare wheel well for all liquids like oils, coolant ... and towing accessories