Towing with a Campervan

We presently have a Unicorn S3 twin-axle and tow comfortably with a Hyundai Terracan (with tuning box) but I am looking at the possibility of towing with a campervan.  I used to own one many years ago and used it for general driving around as well as holidays but nowadays, a campervan alone will not meet our holiday requirements.  We like especially to go for day-outings and could make good use of the facilities of a campervan.  It would also suit us very well if we were able to use our caravan as a base and to be able to go off for a few days with a campervan and then return to base.  So many extra possible permutations would open up.

Question is: is there a campervan out there that would do the job?  I'm thinking I'd need a punchy engine, ideally giving around 200bhp (or whatever they call it nowadays) but opinions would be much appreciated.  I believe there are VW based campers that fit that profile, even having FWD as an option, although lots of money.  Another factor to consider is in buying a campervan, it would almost certainly mean a diesel engine but where are we going to be in the next two or three years with those?  Don't want to spend a sizeable amount on a campervan only to find the value fall off because of new anti-diesel legislation..  Re. the latter point, van converter firms must be tearing their hair out with worry!