Nathan,
When I plan to sit for the whole day, I really, really try to find a tree I can put my Summit in. I have the Python I believe. I've taken all the extra "bars" off it so it looks like any of the open front ones like the Viper.
I think the key to the comfort is the backrest part of the seat. So much so, I bought an extra seat to covert a Lone Wolf climber at some point.
If you can find one of the Summits that folds flat I think that would be the ultimate. Whatever you do, get the open front; don't think you need the "sit and climb" capability. You are young and fit--if I can use my Summit as a hand climber, you will look like a squirrel going up the trees :D
With that said, I sat 3 days last week all day in my Lone Wolf Assault...it wasn't as bad as I remember!