Craig,
We went to the Interlaken areaabout 4 years ago and it was one of the best holidays we have ever had.
We stayed at The Lazy Rancho which is only a few minutes walk from the town of Interlaken.The owners speak perfect English.....and have a small shop on site with basic groceries.The scenery which surrounds you is awesome!!
Whilst we were there a new toilet block was opened...with top class fittings.You are shown to your pitch......we were there in May when it wasn't busy,so had plenty of room.
None of the mountain passes open until June because of the snow,but there is so much to do and see.
As you have been told already,The Jungfrau trip on the train is a MUST even though it is expensive.And the Schilthorn (which featured in one of the James Bond films with a revolving restaurant at the top )
Remember,that you have to have a vignette for your car and also one for your caravan when using Swiss motorways or you will receive a heavy fine.
Web-site for the Lazy Rancho is:-
www.lazyrancho.ch
It also features in the Caravan Club material.
I could go on and on!! Road systems in Switzerland are excellent.