elcoyote
Supporting Sponsor, Overland Certified OC0004
Looking at one of those pictures from the rear it appears that the supports angle out slightly which will likley increase outward pressure on the shell (seems logical but I'm no engineer). The shell being attached to the bed rail will put outward pressure on the bedsides which may cause problems. There have been reports (with pictures including here on expo) of the metal part of the beds in the Tacomas cracking from spreading. Since Toyota went with the wonky two part bed system they dont have as much tying them together. I'm thinking some sort of brace may be in order for the beds.
In our observations driving the Tacoma with and without the Habitat on it, we noticed that the bed stiffened up with the Habitat on it. We believe that this is due to the reinforcements we have added to the Habitat for the cantilever bed feature. We did not see any splaying of the bed sides with the bed under load that you are concerned about.