Truck camper build.

Hey all. I'm new here so please go easy on me. I am trying to learn before I dive into budget or effort wise on a truck camper build. Let me lay out the requirements.
I have a 2004 F150 4x4 with the 6.5 foot bed and super cab. My wife and I are both heavy so a traditional truck camper, or commercial pop up truck camper won't be strong enough. I have been wanting to take my Leer 122 and turn it into a sleeper with a platform bed with storage for the port o potty, water jugs etc.. underneath, but find even with the 122, headroom isn't enough for me to sit up in the bed..
I came across the idea of foamies, and was pointed here. I have been experimenting with polyiso foam and fiberglass, and while it beats other types of foam, I have concerns for strength. I am considering making a, well for lack of a better term, tall box camper shell for my truck. The foamie construction would be great for weight and insulation properties, , but one of my requirements is that I can and will have an air conditioner. A 5K BTU window unit from Walmart will cool the space I want and then some.
I have seen a guy jam a queen bed frame and a short mattress in the 6.5 foot bed of the truck under I think a tall lance cap. Again headroom. I want to be able to sit up in bed, play a hand of cards or whatnot should we get socked in by bad weather.
So how do I even start doing this?
I have a 2004 F150 4x4 with the 6.5 foot bed and super cab. My wife and I are both heavy so a traditional truck camper, or commercial pop up truck camper won't be strong enough. I have been wanting to take my Leer 122 and turn it into a sleeper with a platform bed with storage for the port o potty, water jugs etc.. underneath, but find even with the 122, headroom isn't enough for me to sit up in the bed..
I came across the idea of foamies, and was pointed here. I have been experimenting with polyiso foam and fiberglass, and while it beats other types of foam, I have concerns for strength. I am considering making a, well for lack of a better term, tall box camper shell for my truck. The foamie construction would be great for weight and insulation properties, , but one of my requirements is that I can and will have an air conditioner. A 5K BTU window unit from Walmart will cool the space I want and then some.
I have seen a guy jam a queen bed frame and a short mattress in the 6.5 foot bed of the truck under I think a tall lance cap. Again headroom. I want to be able to sit up in bed, play a hand of cards or whatnot should we get socked in by bad weather.
So how do I even start doing this?