Many of my kayaking friends have small campers , mainly based on VW T4 and T5 , as per Tim's.
There are several watch points , firstly do you want to stand up inside when it is parked , in which case a High Top conversion is essential.
Secondly how many berths do you want , this will largely dictate the size of vehicle you need.
Thirdly , how much cooking/washing etc do you envisage doing inside the vehicle. If using pubs etc for meals you can get away with a much smaller cooker.
If going for a shorter wheel base version , specify swivelling "captains chairs" for the driver and passenger , this will give you a lot more space inside as you can use them facing rearwards.
It is strongly advised to get one with electrical hook up capability, and a leisure battery. This will give you total flexibility in the facilities you need at a campsite.
A conversion is tempting as you start with a lower cost vehicle (and as Tim says professionally converted ones do hold their value) but don't underestimate the amount of work needed to make it "habitable" and comfortable.
