Another battery question

I know that this has probably been beat to death but it seems every where I look or anyone I talk to I get a different answer. Bought the camper with group 27 sealed batteries and they are dying so looking to replace. Camper is an 08 AF 860. I've read that I can fit group 31s in the trays and it looks like it by the measurements (10"h x 14.5"d x 13" w). It's hard to find group 31 in AK as most places stock 27. I did find some 6v at Napa that are part number 7204 or I can order 31 AGM for $400 for a pair from Universal shipped up here. They say 9.75" high though so not sure if that is to the top of the plastic or top of the post. Normal wet cell deep cycle batteries that you have to service up here are about $185 a piece. So which type of battery should I go with? The 6v from Napa, the 12 v AGMs group 31 or 27, or deep cycle wet cell 12v I can get around town? Thanks for any help still a newbie trying to figure out this whole camper thing but it is fun.

Edited.... Sorry there wasn't really a question in there I guess.