You can use my Square Door Tank Calc for the CC volume.
I looked through your images again today. I really like that rear jack idea, how much is a flat bottom crank jack like that?
I may do something like that or maybe a swing out style like the ones they use on a pop-up camper for rear stability.
When I mounted my FB, I changed the design from a round tank to a square box made of 1/4" plate and forgot to adjust
my placement for the added tail weight. Now I am looking to find a way to add nose weight without the ugly visuals.
Currently I am using an old rotor from my Excursion, tossed on the nose of the trailer. It keeps it from tilting, but it's ugly.
I think the rear jack will fix that for me. Though I built mine on a trailer, it is mainly for the ease of moving it around the
yard, not for towing to places.
Looking good, can't wait to see some of your Q! I have been running mine every weekend since completing it enough to cook on. Made 3 racks of ribs and bunch of Jamaican Jerk chicken wings on it this past weekend. This weekend is a friend's birthday party on Saturday as well my daughter's engagement party on Sunday. Love my new smoker, hope you end up as happy with yours as I did with mine!