In my first post on the forums, I shall answer for my mum (chrissiefiddle) as she is otherwise occupied with recovering from an operation.
My mum and I (well me mostly) rebuilt her campers interior last summer from scratch, using the previous interior as a rough template, with modifications where we wanted them.
Photos are in the garage, if we can still get to that?
I decided to use a frame made of 1x1, 1x2 and 2x2 battening, for strength and simplicity. This also enabled me to build most of it outside the camper, where there's space for all 6'2" of me (which there isn't in the tintop camper).
We used 9mm MDF for doors and front, 6mm for sides and shelves. We used 12mm melamine clad chipboard for the work surface and cooker cover.
We painted the bare mdf with a pva/water sealant, then with light blue silk emulsion. This needs another coat yet, but is holding up well to wear and tear.
We went for LED MR16 lights, as they can be driven either straight from the battery or from a 240V transformer, and are extremely efficient so put very little drain on the battery (we do 2 weeks a year camping on a site with no hookup). I created a L shaped pelmet to go at the roof/wall corner above the cooker/sink/worktop to take 3 LED lamps, and this looks smart and also hides the gubbins of the unused right hand sliding door. There is then a box over the bed with 2 led lamps and 2 speakers, this previously also had storage space, but we raised it up to create more space (the whole family are tall!) and to improve the view from the rear view mirror and in raising it we lost any useful storage space. (However other bits of the redesign opened up more storage, so on the whole we gained).
We have discussed a water tank and pump, and there is space to do it, but we haven't fitted one yet.
Feel free to ask more
