I think the long sides could be made with 1/2" or 3/4" plywood (obviously the short side 2-bys would be wider) to save weight but still have loads of strength.
Seems right, especially with the added tow package on the AWD. Still, not too shabby. In fact, at those MPGs, the difference is almost statistically insignificant. Hand grenades and horseshoes...
Yes, I remember driving an early Prius (second gen, as I recall), as a rental. My '89 Tercel Wagon (the real square-ish one with 4wd) was the most underpowered vehicle I've ever owned (but indestructible), and it might have been speedier than that Prius.
I've done many of the M&M (Mabett & Maxina) Maverick Modifications, as well as others that are not alliterative.
Mabett:
Mudflaps and rear wheel splash shields (I kinda consider those mudflaps too)
Door storage tray inserts
Front underseat storage bins
Dashboard organizer
FITS dual rear cup...