Need to purchase 2 batteries by Friday...help

[Diesel Pusher]

I have had some work done on my camper over the winter. I converted the disc brakes to electric drum brakes. I had to replace my univolt converter as the original one was not working...don't know why. I also had to get two 30 pound propane tanks installed with a new type of valve.

Anyway, I am going to pick up my rig this weekend and the man doing the work mentioned for me to purchase 2 deep cell marine batteries to install in the two separate compartments which are in the front of my rig accessed behind the old master brake cylinder compartment. When I purchased it in October, it had no batteries.

What size batteries will fit in there. I saw some at the store that said a group 24??? and some that said a group 27???

I planned on buying these batteries from walmart from the recommendation of the man doing the work. He said they would be fine and if I were travelling and needed warranty replacements, Walmarts are everywhere. Makes sense to me.

Can anyone out there recommend which battery to purchase there and what size?

Thanks for your help.

Rob.