In reply to MattH:
Hi Matt, I am doinga little bit of work in the camper industry but not on this subject, yet I do have to know about regulations etc.
When a seat is fitted with seat belts you have to have a metal supporting frame (this does not have to be crash tested) and the fixing points have to be reinforced through the subframe of the vehicle.
Putting seat belts in for you would not be the issue as it could be done even on the side facing seats. The issue you are going to have is the MOT. I understand that by law they are not needed but if they are fitted they have to be tested under MOT regulations and with the design of the vehicle, this would be the downfall. It would fail an MOT because of the seat belts.
You may be able to find a good converter that would be able to re-arange the design layout of the seats but this will come at a cost. When buying camper / motorhome they sell them as a 2 berth for a reason and that is that they will only be able to sleep and carry 2 people safely.
I am sorry if that is not what you wanted to hear but I am sure you will find it is correct.
I hope you somehow sort the issue out.
T