Thanks for expressing the thinking behind much of what you have done. You are right about me probably not using my rig in the same way you do, but our concepts remain the same. Keep it light, but durable. Keep the weight we carry low. As I stated early in my post I believe in preparing for 90%, not 100%, of what I MAY encounter and I change my plans when I encounter the remaining 10%.
Last night I watched Tim's video on his cabinet build, so with his experience and Vic's, I'll go with 1/2" in the cabinets. My overhead is longer than the original Grandby, but shorter than yours. At the back of the cab my bed rests directly on the Jeep top which I have supported directly on the roll bar and since my camper is a permanent mount it can be supported at the front as well by my light bar, so I may try 1/2 there also, but I am in the 250 lb range!
Like you suggested I'll wait until I get further along in the build or even after I start using before I decide to add airbags to the rear.
Keep the rubber side down,