Do you have other charging sources like a genset? If yes how much can/are you willing to use it? Where are you camping with only 12 hours light in the summer? Or are you thinking 12 productive hours?
I have a 22' TT. If yours is like mine I have room for one largish panel in the middle and 2 long stripes of space down the sides, but layouts vary a lot. What matters is the specific shape of the spaces you have open, and how they will be compromised by shadows from things like AC.
A lot of people run a ratio of between 60% to 100% watts in panels to amp hours of battery capacity.
Jim