I have a nearly new Transit Custom DCIV L2.
That means rear side windows, seats and long wheel base.
I removed the standard rear seats and bulkhead, and fitted the 2nd row seats from a Tourneo.
These both fold up and are removable, just unclip from the rail.
The tourneo seats and floor cost me 500 quid. They are almost new, removed from a tourneo by a company that does taxi and disabled vehicle conversions.
Sold my original floor/seat/bulkhead for over 500 quid
As a guide, when I recently picked up my Pani, I simply folded the centre seat forward, fitted a bump in wheel chock behind it (uses the seat to stop it moving about) and the Pani goes in easily clear of the rear doors. Held in with one of the handlebar strap things and a tie strap on either end of it.
I've had a whole bunch of bikes in the van. With the seats folded forward I can easily get 2 road bikes, or 3 off road bikes in.
We also have a stand alone kitchen pod, containing hob, sink, and all it needs (gas bottle, clean and waste water tanks, plus a battery for the water pump).
This is secured to one of the floor rails, but can be lifted out by one person if necessary.
I've designed my own rear seat / bed. Its steel box section, and can either be folded up against the side of the van, or removed completely.
So if necessary I can have a bike in the van and still sleep in it, or unload the bikes and have a double bed.
I've also fitted mains hook-up and a diesel heater, as we use it as a camper with a drive away air awning too.
Sure I could have bought a bigger van, but this is still small enough to fit in a normal parking space, and get in multi story car parks and height barriers.