I have a '91 3 door x-MoD 110, and camp regularly in it with two (and once 3) people in the back.
I have 4 sections of .5 plywood that goes across the seat boxes topped with a 4" piece of foam. I use load straps to keep the boards tight. Under neath i have 4 large ammo boxes, with ropes attached so that i can pull them out. 1 box for food stuff, 1 for cooking gear, 1 for clothes and the other for misc. My cooler sits strapped down while travelling, and moved to the front while camping.
The side lockers hold extra fluids, recovery gear, air compressor etc.....
With 2 people (under 6') it is actually very comfortable....3 is quite snug, and probably wouldnt so it again...but it was me and two female friends so maybe.....
1991 Defender 110 300Tdi x-MoD 19 KK 88 - daily driver
1955 Series 1 86 Hardtop 173601415 - undergoing the infinite rebuild
1955 Series 1 86 Hardtop 57130577 - just a pile of parts now
1965 Narrow Track Sankey 35 ET 73
1985 Series III 109 x-MoD BATUS 77 KC 63 (sold)