Ahhh, the old motorhome debate...
Robbo - just to set the record straight, a 36ft Infinity double slide home with 7.5kw generator is not a "camper" in our books!!!

I think you need to know which campsite you will be using before you decide. Houx is only one with full hook up. Hook up on MB is subject to suitable bribes to various toilet block attendants, Smokie, George, Mark, Tracy and others!!
Unless you have a hire budget of £3-4k, a decent on board generator with any gumption will not be possible.
So, I suggest if you have no hook up (likely) go for a transit van motorhome type (known as a C class). This will have gas fridge, gas water heater and plug in should power be available. Cost maybe £1-1.5k Add a hired genny for £150 and use this for power for stereo, pool fountain, fairy lights etc. Only down side is noise, but you won't notice after Staurday anyway...
Re: water, most folk will offer you a top up from a nearby hose in exchange for a cold beer from the fridge in your 'home. Otherwise bring a tap splitter and a long hose, say 60m minimum with jubilee clip on the end so you can install semi permanently.
Best of luck