I have two SEARS group 31 rv marine AGM's that have supplied us with lots of reliable power. Installed a 4 gauge charge wire to the TC batteries off the truck alternator and through a big constant duty solenoid. One of my best and biggest pay back TC modifications.
There are others that don't justify the cost of AGM and go with 2 wet cell 12 volts and some go with 2 6 volt golf cart batteries.
2 12 volt batteries, you have power if one fails.
2 6 volt golf cart batteries, no power if one fails.
My 2 AGM's were about $500.00 which was an easy yes for me.