I had been driving a Tacoma since 1996, and it was hard trading it in - especially given gas prices.  But the extra room in the double-cab is great, and the bed of the Tundra is longer, which was important since my 6'-0" frame wasn't going to fit comfortably in the Tacoma's bed.  An extra benefit is that the wheel wells of the Tundra aren't as high as in the Tacoma, which would allow me to build a platform lower to the truck bed, which in turn provides extra headroom.

I've had a spray-on liner in all of the three trucks I've owned since '96.  Worth every penny.  It's practically indestructible, and even after the serious abuse of hauling rocks and boulders for landscaping, it rinses out and looks almost new.  I was tempted to pass on it this time since I was planning to put the cab on, and build the sleeping platform, but I figured this would help keep things from sliding around once it was all in place.

With the bed liner, I didn't really need to put carpet down before placing the wood beams, but I'm hoping that this will help keep vibration sounds to a minimum.  I got this roll of 6'x8' outdoor carpet at Lowe's for about $15.  It has a rubber backing which will help keep it in place.

I cut out a roughly sized piece of the carpet, and then traced the outlines of the tire wells and other parts of the bed.  The carpet is a 14 oz. carpet, which was fairly easy to work with.

This part took the most planning, and was more time-consuming than I had thought it would be.  For the beams to be stable, they had to fit in the grooves of the corrugated truck bed, which meant I couldn't space them at exactly the interval I wanted.  I wanted the rails spaced just slightly wider than the containers (purchased at a local container store) to prevent the containers from sliding around too much. 

I decided to go with 1x10s and a 2x10 for the beams.  (A little later, you'll see why I went with a 2x10 for the center beam.)  That provided plenty of storage room underneath, and would still allow us to sit up on the platform once the cab was installed.  10" beams meant that the containers had to be less than 9" tall (note:  1x10s aren't 10" tall!  I had to return some perfectly sized containers that were 9.75" high and go with these that are about 8".)  Once I had the containers, I knew where to place to the two 1x10s. 

I bought some smaller containers for the front of the bed that will be accessed via a couple of hinged doors once the platform is completed.  There is still plenty of storage space between the bed rails and the outer beams.