Made some progress on the bump out for my feet. I have used an Accuride slide that is made for cutting boards you pull out from under a counter top. It has a positive lever lock. I can pull the bump out all the way out till the lever snaps into a lock position. That holds the bottom in place.
Here is a shot showing the slides mounted in the bed slats. These slides are not meant to support much weight. They are more of a guide and a stop for the bump out.
To keep the top snug to the side of the trailer I used some toggle clamps. There will be a gasket on the bump out that will be compressed by the toggle clamp. Now both the top and bottom are secured to the trailer with a water barrier gasket.
The gasket will be full length when it gets installed permanently.
There will be a door that is hinged with an aluminum hinge on the top. The door will swing up and the bump out will pull out. Then the top will drop down onto the bump out. There is a 10 degree angle on the bump out sides, so the rain will run off. This picture just shows a small piece to show how the door works. There will be gaskets installed on the frame work where the door closes to keep water out when closed. There will also be gasket on top of the sides of the bump out that will be compressed when the top is secured. I will use draw clamps for that.
Because of the thickness of the floor of the bump out and the fact that it has to slide over the mattress floor there is a 1" difference in the bed deck height. So the mattress in the bump out will be 1 " thinner. Being it's just my feet in there I will not notice that. I did this is a past trailer and it worked out fine.
My plan is to make the mattress in 3 pieces, with the cover sewed so it will fold like an accordion. Hopefully this will allow me to keep my bedding sort of made up when in transit.
Tomorrow the skin and trim go on. I'm finally seeing the finish line.