Hi Edwina,
I guess by adjustable height hitch you are talking about a hitch like this http://www.brookwell.co.uk/acatalog/STC50256AA.php if so when you finish towing you can just take the pin out and it off it comes, all you are left with on the vehicle is the main drop plate but no ball and plate..
The only downside to this type of hitch is they tend to rattle a bit when towing, but you should be able to get the van level when towing.
Martin "E"