In reply to dan bulman:
In Switzerland, you might take in the Walensee on the way over from Austria. Sitting below the towering cliffs of the Churfirsten, it is perhaps one of the lesser known scenic delights and easily accessible from the motorway. At the eastern end, Walenstadt has a lakeside restaurant, a refreshment kiosk and a large grassy playground.
I'm not sure how feasible it is to drive over the passes in your campervan, but to get from there over to Interlaken, the Klausenpass followed by the Sustenpass would be one option (perhaps not both passes in the same day!) , while replacing the Sustenpass with the Brünigpass would be an easier drive. The Klausenpass road is quite narrow and challenging at points as well (the whole western side of the Klausenpass isn't available in the Street View coverage of Google Maps...which is fairly restricted in Switzerland for security reasons or something!).
The Klausenpass has a small refreshment stall at the pass itself and a larger hotel restaurant just down on the west side of the pass, both with large parking areas. If taking the Sustenpass, one has to be aware when coming south from Altdorf on the motorway that this is the way to the Gotthard tunnel, and traffic jams of several km are commonplace: best to get off the motorway sooner rather than later, at Amsteg for example.
The more southerly route via Chur, Oberalppass, Andermatt, Furkapass, Grimselpass is a longer alternative.
Innetkirchen, at the foot of the Grimsel and Sustenpasses has several campsites and would be a (much) quieter alternative to Interlaken, but Grindelwald should not be missed. Or else the main goal would be Zermatt and the Matterhorn, unless you can fit both in.
There is a good on-line map of Switzerland here: map.geo.admin.ch.