When I was a Squaddie (many moons ago), I used to buy UK RHD Tax Free cars. Any warranty work required (regardless of manufacturer) was carried out by my local dealer here in Germany as all the warranties were pan-European, I never had any dramas getting work done, even though I hadn't bought the vehicle locally. I even got the Mehrwertsteuer (VAT) off the price of servicing. I don't see why caravans would be any different as long as there is a network of UK dealers. I might struggle with my Tabbert in UK as I don't think they are sold there but Adria, Hobby etc do so I can't see it being too much of a drama.
In fact I know it isn't a drama with cars because we once visited the UK in a German registered VW and the engine warning light came on. I took it to Hayseldens VW in Barnsley and they sorted it under warranty. No problem.
How much is the Knaus Lifestyle (the four berth one) in Germany? Last time I tried to look I got some Dutvh prices but they didn't look all that good. I think I might not have searched very well though.
the Adria prices look a lot better in your neck of the woods.