At 18mm the plywood you are using is 3 times as thick as the plywood currently in use for Eriba bed boards.
Randa

On our first Eriba I made a fixed bed. I used lengths of prepared 3x2 and 9mm or 3/8" plywood in several pieces. One piece will be difficult to move into place. 18mm is also more than you you need. You will need 50mm holes cut with a hole saw to allow the mattress to breath. I used a domestic mattress and cut a piece of upholstery foam cut to the profile of the back of the van. My adaption simply sat in place and did not have gas struts to lift it as I had access lockers on both sides of the van. With this set-up weight was not an issue.

Colin

No, sorry, I sold the van back in 2006. From memory:-
- Cut two lengths of 2 x 1 to length and use a couple of quick grips or G-glamps to hold these in place along the front top edge of the seat bases.
- Cut 5 length of 3 x 2 to length that will sit on top of these and run from one side of the van to the other,
- screw through these into the first two battens and remove the clamps, result is a framework braced into place that cannot move.
- cut your 9mm plywood to shape in pieces that will allow you to lift and slide them around to access the space under the seat bases. If need be screw through the edges into a 2 x 1 supporting batten that will offer support to the edge of the next piece of ply.
- drill some 50mm holes on a 10" grid to allow the mattress to breath.
- do not bother with varnishing
- source a 100mm thick foam mattress from the likes of IKEA if possible to fit the majority of the bed gap. This might be difficult as I think you need a UK size to fit the width of the Eriba.
- make a template for the curved end gap filler you will need and get this cut at an upholsterers, when they open up.

If you have access to a bandsaw then you could easily cut down an oversize 100mm thick foam mattress and fit it back into it's loose cover, tucking the cover down the edges as needed

PM me if this needs clarifying.

Colin

Formby on Merseyside, midway between Liverpool and Southport.

Colin

You could get into making toy cars with all those 50mm wooden wheels you'll end up with.

Colin