First thing to sort that wandering urge on the motorway is to get an OEM chin spoiler on it - will help a lot.
As for suspension, you'll need to check compatability because yours is an early bus, so has different front suspension, but *if* they fit, go for some later Caravelle springs, which are -30mm and OEM Caravelle dampers - sorry but I was a Syncro driver and the front suspension's very different!
Prickwerks do various lowering kits, but it's a camper you may want to take it in and out of fields - lowering too much would be a stupid thing to do. H&R or Bilstein dampers on -30mm springs should firm things up nicely and get the damping tightened up to suit. 2t is a lot to punt about on crapped out 25 year old dampers thus a new OEM kit will make a world of difference!