Many suggestions above will work fine for you. Some of the reasons are a little suspect.
Batteries are designed for different uses. You definitely don't want an automotive starting battery for use in a TT. You want a "deep draw" battery, but there is not clear definition for what a deep draw battery is other than it is designed to be drawn down slowly over a long period of time.
Sometimes the plate thickness is cited as better for deep draw. The thicker the plates, the better deep draw performance is expected. However, the thicker the plates, the higher the internal resistance. The longer it takes to recharge and the slower it will discharge.
The typical testing procedure is to determine how many amp hours the battery supplies when drawn down over 20 hours. So amp hours is the defining factor. This test is repeated until the amp hours supplied is down to 80% of capacity. The number of charge/discharge cycles is the "life" of the battery.
If a Marine battery has a longer life than a gulf cart battery, then it is a better "deep draw" battery. It all depends on the design. Look at the battery specs to determine the performance.
AGM batteries have several advantages over flooded cell batteries. They do not vent flamable hydrogen gas while charging.
They do not spit acid or spew acid vapors causing corrosion of battery compartments.
They are better for deep draw situations, because they are not damaged by drawing down flat. Their chemistry stops the discharge before damage is done.
They are better for dual purpose such as starting a generator as well as supplying long slow discharge travel trailer house power. AGM's tend to have thinner plates that discharge and charge faster.
Flooded cell batteries have an advantage too. They can be overcharged with little loss. Just add distilled water to fix them. AGM batteries will vent if overcharged there is no way to replace the water that is vented.
I use a pair of 100 amp hour Interstate AGM batteries. The 200 amp hours last for 5 days of dry camping and leaves a good size reserve available. I expect to get more than 10 years of short camping trips with a few long trips sprinkled in. My last pair were working fine when I sold the camper after 10 years of use.
Battery University https://batteryuniversity.com/
How does the Lead Acid Battery Work?
https://batteryuniversity.com/learn/...ased_batteries
Charging lead acid batteries
https://batteryuniversity.com/learn/...d_acid_battery
AGM
https://batteryuniversity.com/learn/..._glass_mat_agm
How to Charge and When to Charge?
https://batteryuniversity.com/learn/...o_charge_table
How to Store Batteries
https://batteryuniversity.com/learn/...tore_batteries
Summary of Do’s and Don’ts
https://batteryuniversity.com/learn/..._battery_table
I wish you good luck and happy trails ahead!
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