Get one of the spider web things for holding things down in the truck bed. It has about 8 hooks and is stretchy ( is that a word??). yu can block the whole area so he cannot escape.

If you look at Lance camper's website, they have a fold down bunk and child restraint. It is a mesh enclosure. I personally think this is the best solution. Maybe you could contact a Lance dealer and see who the manufacturer is.

years ago, had a class c with bunks as you describe-I used the table leaf from the dining room table,(the one in the house) worked great! during day, just slid it back, or would lay it flat under the mattress. Dona

http://images.google.com/imgres?imgurl=http://trusca.im...s%26um%3D1%26hl%3Den

This is what I use for my kids. They go between the mattress and the base. They can fold down and are easy to remove.

We used 'lee cloths' on our boat to keep people in their berth during heavy weather at sea. They are pretty simple to make.

1. Make a piece of canvas nearly as long as the bed and a foot or so high. Install a number of grommets along one of the long edges of the canvas.
2. Install some hooks on the overhead corresponding to the grommets in the canvas.
3. Attach the canvas to the plywood under the bed with a row of screws, near the edge of the bed, but so that the canvas can lay under the cushion when not being used.
4. Lace the grommets to the hooks overhead.

You can leave a little room at the foot end for ingress/egress.

Another alternative is to use a board that fits in a slot at each end of the bed.