My rebuild design is now for a full size queen along the back with the corners of the Argy squared up with shelves like the ledges for the old gaucho up front.
Full size twin mattresses too for the bunk I'm building streetside.
Yes, the interior length of the Argy is 22'...so there's lots of room to play with. So the mattresses will fit, but the full mockup will tell if the new design layout will work ok.
The only thing bugging me now about the design is the "climb over" wife bit to get in and out of bed...but that may not be a bad thing .