Doesn't matter what the caravan is as makes no difference. It depends on what you want the battery to do. powrtouch recommend no smaller than 85a I think. will you be off grid or always on EHU as if off grid the bigger the better.
I have a 2008 Coachman 550/5 with powertouch, just fitted a Numax XV 110ah, it replaced my old Numax battery which had been on since caravan was new so i saw no harm in replacing like with like.
Stumccly
Caravanner