It's threads like these that give me the confidence to tackle jobs. I did my rear crossmember last year and tried my best to get between the top of the chassis and the tub. I did think at the time it would be easier if I could get the floor up. Now I've seen how you've tackled it I'm considering lifting the rear floor replacing the spacers and re painting.
Looks good.
You can get a tent you back up to & attaches to the rear of the LR.you can stand up & cook,etc
There was a company that made water tanks for the arches of the LR.
Marine tanks are 70 litres & you cut your own inlet/outlets
Used push fit pipes on the water system. Used the inlet & outlet(outside) to attach external shower. Also added a 12v pump point(external) so can fill the tank back up from a bucket.
Also ran a pressure switch/pressured pump In the water system. Saves wiring taps up