Thanks. No, I have not measured anything thus no false or correct impressions. I also do not believe that my van is overloaded.... 2 people traveling, no trailer hitch or bikes. Still, It is also impossible to drop the spare wheel without lifting the van with a jack. So... a few cm more clearance, especially in the back would be nice.
I take your expert word that lifting just the rear is not advisable. Maybe easy and cost effective but not a good idea as you write. I accept that. Too bad that you have not offered that answer to start with. No, I also do not want to lift all corners altering the entire suspension. That would be "playing with the suspension" beyond a reason. (BTW, in my previous T4 camper things were much easier to adjust.)
So, another thought is to change tires from 235/55/17 to 235/65/17 gaining almost 3 cm clearance in the process. Here in Germany, that would require buying special expensive wheels (homologated for that size tire) and still having our TÜV issue their judgement and adjusting odometer specs. For a fee. Complicated.... but as you call it in the UK, swampers do it all the time. Not my gig.
What do you think about all that and WHY?

Am I stuck with the van the way it is? Anyone have found a solution? Thanks.