If you want the benefits and cost of an AGM battery I'd go with Concorde Lifeline. About $250 shipped to your door. Lots of size choices. Very low self discharge, much lower than a wet cell, important if you leave your trailer unplugged for months at a time. More tolerant of deep discharge but that's not good for any battery. Good if your battery is hard to get at so you will forget to check the water.
Get a good three stage battery charger with at least C/10 output, i.e. an 80 ah battery wants at least 8 amps during the bulk charge phase.
Estimate your battery usage in a day, for each device, amps x hours turned on, add up for a 24 hr period. Then times number of days between charging opportunity, then times 2. That's the battery capacity you need.
If you are running 120v motors (like a fridge
compressor) with an inverter you need to pay special attention to start up loads. Basically you will need more battery in that case.
I use AGMs in my electric boat because watering would be a huge pain and rocking might cause acid to leak out. I use 2 Trojan T105 6v wet batteries in series in my lil'snoozy.