Of the battery choices out there, a conventional flooded cell will be the
most tolerant of use and abuse and provide the longest life. Most of the
12 volt deep cycle batteries or beefed up starting batteries and still
have short lives of one or 2 seasons. The golf cart batteries are a lot
more tolerant of heavy use.

Of the common, reasonable price brands, Trojans are probably the best.
Best plates and a lot of active material in the plates. Yes there are
better such as Rolls Surrette but bring money.

AGM and Gel batteries is still emerging technologies and the advertising
is a lot of hype. While sold as sealed, they are truly sealed. All of them
have some type of pressure relief vent.  Temperature changes can cause the
vents to weep and once the electrolyte is lost it can not be replaced.
Most cell failures are the result of dry out. Unless you truly have an
application requiring a sealed battery, they are not worth the money.

Any battery can boil, off gas from a failure, whatever. For an RV
application, the batteries should be installed in some type of sealed and
vented compartment, especially if you plan to sleep while the batteries
are being charged. This is not always practical so consider a flammable
gas detector. They will pick up hydrogen. Plastic battery boxes are
available for most any sized battery. They can be placed under the seat
and you can install drain and vent of desired. At least if a battery boils
out, the acid will be contained.

For wiring and charging, the circuit needs to sized for both charging the
battery and any load connected to it. This includes inverters. The GC-2
will pull about 40 amps off the alternator during the bulk charge. Add you
other loads. Best results will also be a direct line from the alternator.
#6 gauge. Also, you want a truly reliable relay. Most important that it
disconects when expected. You want double break contacts like in those
solenoid type cans.  Not a small lighting relay.

Dennis