AGM is what you want, they are designed to handles same charging characteristic as your cheap flooded battery.
Gel cells are more critically charged and your RV charge system will cook them off and destroy them.
You don't need to worry about venting AGM batteries and they can even be layed on there sides or on there ends and used if you want. As long as you don't run them down below a 50% charge before recharging them they will last a long time. I have 3 12volt for a total of 435ah on 520 watts of solar for my boondocking.
2014 Palomino Columbus 3650TH
435AH 12V VMax Charge Tanks, 520 watt Monocrystilline Solar Array, Morningstar MPPT TS-60 CC,Morningstar Remote,Cotek True Sine Wave Inverter,Cotek Remote Controller,50amp Progressive Hardwire Surge Protector
2015 Dodge 3500 6.7L 4X4
2011 CanAm Commander XT 1000