Hi Paul - welcome.
It's really heartbreaking when your dream van turns out to be a nightmare!
After this length of time, it would probably be hard to reject the whole vehicle under Sale of Goods law, although it could be worth starting from that position with your dealer. You'd need to be able to argue that the van was either "not of merchantable quality" or "not fit for purpose" from the beginning, and that you've only left it this long to give them chance to fix things.
Short of that, for the sake of his reputation the dealer may be willing to give you a better-than-otherwise deal on a change - but make sure it's genuine! Prices on forecourts are always negotiable anyway, so you'll need to be convinced (perhaps by looking elsewhere) that you're getting a significantly better deal than a new person walking in off the street!
Other possibilities:
The converter's (not base vehicle) warranty: check what it covers, and for how long. It may only be a year, but many big converters offer longer. But even so, by this time, this would only help in getting the faults fixed, not replacing the van.
Similarly, the manufacturers of the individual appliances may take an interest (or even in the case of the leaking fridge be liable!), but their actual warranties will almost certainly only be for a year.
Note: I'm no legal expert, and if you really want to press for your rights you'll need to take proper advice about just what those are!
Best wishes with this - and please let us know how you get on.