My son did basically the same thing with his 1999 Tacoma:
Here is the link:
Tacoma Sleeping Platform, Carpet Kit, Camping Setup - YotaTech Forums
His reasoning is pretty sound in that he didn't want a trailer of any kind (no storage at his college, which is in the Shenandoah Mountains), he and as importantly his stuff can stay dry in really inclement weather (he either sleeps on a pad in the open or in a small tent on during nice weather), his girlfriend is very much a hiker/outdoors gal but likes a comfortable place to sleep and, on long trips, he can pull over at any Walmart and get some sleep.
He can also comfortably take all the gear required for extended trip effortlessly beneath the sleeping platform.
He also borrowed from this site, which is linked above:
http://www.bajataco.com/Camper1.html