Another good plan, Paul. And, I like your approach of taking actual measurements of your son in a sitting position, etc. That's the only way to know for sure if your design is workable or not. Allowing for 7-footers seems a bit of a stretch when we're playing a game of inches, but you are the only one who knows your needs and wants. Not me.
That being said, if you want the best camper then what you should build is a carbon copy of what I did!!
I'm in the convertible bed/gaucho/dinette camp. Multi-purpose "furniture" has numerous advantages and has always been incorporated in small campers for good reasons. Others object, claiming they don't want to fuss with converting each time. A fixed bed isn't only for sleeping. Will you, or someone else, be satisfied sitting on the bed edge for hours at a time or only short periods? Do you ever sit where there's no backrest, such as in the bleachers at a sporting event? For hours? Does that bother you? It, again, all depends on what you want, not what anyone else thinks you should have. How many people will use this? What are their heights? What inside activities do you have planned? Card playing? TV watching? CAD design is fun and addicting but if the occupants and their activities aren't taken into consideration, you'll not be pleased with what you build. You seem to be taking the practical usage into account... good. I enjoy your enthusiasm, reminiscent of your first build if not more so.
The forward or aft dinette position w/radius profile: Standard design on canned hams and other campers, we've got examples too numerous to count. Tried and true. Why? Ergonomics 101. Ever try to stand up after you've entered the dinette seating area? Impossible without breaking your legs. You're forced to begin the crouching position as you seat yourself. Upon leaving, you first slide out and then stand. We do it automatically without thought. I'm 6' 1" and have never hit my head on the ceiling of DD. I've had four people sit at my dinette table in comfort. No one hit their head entering or exiting. I'm good to go. As I age my posture isn't going to become more erect. When you really think about it... these campers are advantageous to the old, crippled and infirmed. I'm living proof of that!
