As said, definitely do all the sanding and sealing before you fit into van.
Instructions are poor, could hardly read mine, blurred photo copies, total crap.
If you scribe the wheel arches a bit, you can shift the whole u shape unit to the rear a few cm’s, every little helps, to give more space up front behind drivers seat and the sliding door opening.
YouTube channel, ‘Higher ground lifestyle’ is a good watch, he has some tips and adaptions when fitting his furniture.
I fitted the u shape kit and extended the rear top bed slate section right up to the tailgate, so the bed is 180cm long.
I also built units on top of the rear section above the wheel arch, so we effectively have a LShape layout now.
Enjoy making it your own, it’s cheap enough to chop and change these kits around to suit your own needs.