i just did the exact same thing last weekend after going ever all the prices from companies fitting em for you. i thought, its not worth all that but maybe i wish i had overall. i had so many teething troubles it was gettin on my gromits.
heres what i did (if you want to follow my lead!) its working ok now.....
i got a pump and controller for £150 from pure freedom
650litre tank from another shop on ebay for £200 (u might want smaller if you have a small van)
the tricoflex reel at £118 (10pnp) someone else suggested it ok, not brilliant.
a di vessel £80
u need to check your tds from your water you may not need an ro unless it above what 80?
i run it straight from the van battery save you 80 quid on the leisure battery its never took anything offf the charge in the battery even if your not moving it much.
ratchet straps for £15 off ebay (5tonne)
you'll know how to secure em under the van if your an engineer.
a fused switch £5
and some and some jubilee clips n o rings for securing the fittings.
one thing you have to make sure the pipe is fitted perfect from the tank outlet to the pump, you cant let air in or water out. im sure others will make suggestions different but thats how i just did it and its working well. (now!)