I've just been looking through extra info that comes with the MoT printout, and found that included in the brake efficiency part is the weight on each axle and the total weight.
I now know that the HiCube with about a quarter-full fuel tank, a quite-full 15kg gas bottle, extra spare wheel and camper interior weighed a measly 2710kg at the time of the MoT. I'm assuming that also included the weight of the tester! With that in mind I reckon that loaded with the two of us plus food, clothes and bedding we 'll weigh around 3-tonne. That gives us best part of half a tonne for extra mods (planning for bog-on-board) and cargo (bicycles etc).
Mat