This is a platform I built so I could sleep in my truck and stow my gear underneath.
Step 1: Think About What You Want.
I started by thinking why I wanted to make my truck into a camper. I decided to split the storage area underneath into two halves. One side was for large storage (surfboards, snowboards) and the other side for stuff like (snow chains, camp stove, sleeping bag). I ended up splitting the right side and boxing in the stuff that lives in my truck like(water, sleeping bag) and leaving a easy access area right by the tailgate.
Step 2: Figure Out What You Will Need.
My trucks bed is roughly 5 feet wide and 6 long. I was sure that I wanted a piece to cross the whole width, but I didn't care so much about the length of the bed.
2- 5x5 sheets of 3/4 (birch)
1- 8 foot 10x2 plank (poplar)
A box of wood screws 1 and 1/4 inch
A small amount of wood glue
A sealant to protect the wood
Step 3: Start Cutting.
I have a tacoma and in the bed are small rails that stick out 9 inches high. This was great and saved me a ton of time and inspired me to design the rack a simply as I did. The first cut I made was on one of the 5x5 sheets, cutting it down to 5'x4'9" so it would fit into the bed of my truck. I repeated the cut on the next sheet of ply, I made an additional cut at 11 and 1/2 inches so the wood would go right up to my tailgate. Next I used my jigsaw to cut out a space for the supports of my truck. When everything fit right I put in the access points. I used a skill saw to cut out the holes. I marked them out and cut straight through the deck, I left the corners in and used a hand saw so I didn't leave cuts in the rest or the wood. I had a had to cut the plank to 6'1" and the plane the top down about half an inch so it would fit snug under the deck. I used the left over wood from that cut and I made a side support / way to separate my cargo.
Step 4: Glue and Screw.
I used 3 wide strips of ply to hold up the lids. I glued and clamped the pieces together. Then I pre drilled and screwed them in all together.
Step 5: Make Sure It All Fits.
I had a few problems when I was making and installing everything. The biggest problem I ran into was when I got the shell. The opening was to small to slide it in even on the diagonal. I ended up taking about an inch off the side so it would fit. I filled the gap with a broom stick that has a hook on one end. (for grabbing stuff in the way back of the truck)
Step 6: Sand and Seal.
When you know everything fits the way you want it to you can give it a sand either with a block or finish sander. I used a clear spar urethane to waterproof the wood. I covered the top and bottom of the deck with 4 coats. I sanded with 220 between the last 2 coats. I don't know if this was the best way to seal the wood but it is working so far.
Step 7: Finishing Touches.
In the large cargo area I put padding in the front and back. I used a yoga mat I got from a thrift store, I cut it into rectangles that would fit under the top deck. I double layered them to add a little more padding, I just used wood glue (probably not the best glue but it is working great so far). I added some velcro to the back so I could remove them if I need to.
Step 8: More Finishing Touches.
I put some velcro strips on my snow chains and the wood support (no more sliding around).
I also put some little non-slip sticker things under the panels to make them a little more quiet on rough roads.
Let me know what you would have done different, or if you have any questions why I did something a certain way.