'insane'? No, but I hate to wonder what you are keeping in there normally which has you worrying about temps / theft?
My platform / drawers are ~10" tall overall height. I've still got 25" at the center of the Liftgate coaming and 23" over most of it. I'm able to slide a boxed 50gal water heater or an upside down standard wheelbarrow in there, or a variety of portable workbenches, power tools etc. The cargo area of my Sub has an interior roof a few inches higher than the coaming, stepping down around the 2nd row. The Sub's got just over 8' of room behind the front seats, so I'm still able to load 4'x8' sheet goods.
But all that is beside the point. I've got a 54"L x 19"W x 8"D drawer that is chock-full of all my roadside emergency, recovery, first aid stuff and basic hand tools. That stuff is always in the vehicle
and nobody can see what's there. The other drawer is 9"D and has some prepper stuff and the rest of the load changes depending on what I'm to. They both lock, rifles will fit in the other drawer. 30' pull strap, tie downs, hitches, etc.
And nobody can see what's in there.
I used to keep such stuff in a plastic footlocker. Or in seabags / surplus mil fabric luggage.
Now it's all out of sight. Which is just what I need the 99% of the time I'm in s-hole Los Angeles.