I am in the process of the same thing. I installed the golf cart batteries yesterday and they are charging now. I went with the Trojan T145's. They cost me $99 a piece. They had the most storage of anything I could find that I could afford. The advantage of the high capasity battery is the length of power. The down side is they take a bit of time to recharge. We are planning a trip to Florida on Sunday in our 5th. I am hopeing these batteries will give me the power I need to get heat while dry camping.
Check out the Trojan web site. It will give ya some ideas as to the storage of all the different types. I am told Trojans are pretty good batteries.
One thing to keep in mind, is that 6v batteries tend to be much taller than 12v. Make sure you have enough height in your battery compartment for an even number of them. Trojan is perhaps the standard against which all are measured. Flooded cell batteries are the most reasonable in price, but require the most maintenance and have a limited lifespan. It is possible that some form of Glass Mat or Gel technology will reduce the maintenance and increase the life, but at a significantly higher price and with no tolerance for overcharging. One of the more common ills of golf cart batteries is deposits on the plates reducing their efficiency; this can be prevented by adding a fairly available box (Desulfator) to the circuit. Another way to extend its life is with a 'smart' charger (rather than the dumb charger commonly used in RVs).
One of the key components of battery cost is shipping. Contrary to common practice, check and see what is available locally first. I happened to find a local battery supplier, who's price was reasonable, selection good, and they offered a 2 year full replacement warrenty. If local suppliers can not fill your needs, a good place to start is the various online solar energy companies (like www.mrsolar.com). Once you find what brands/types of batteries interest you, you can then extend your search. Remember, shipping may be a more important factor than the battery cost.
As for amp hours, it is pretty much directly related to size and number of batteries, so measure your compartment, leave enough room for maintenance (a pull out tray is invaluable), and then get the most/biggest battery set that will fit. Remember, you must always get golf cart batteries in pairs, to make 12 volts. However, you can have as many pairs as you want (and can fit in).
One final note: batteries are HEAVY. Make sure you can manage the individual batteries you get for installation or at least for maintenance. Also, keep an eye on the total weight of all your batteries to ensure you don't exceed your trailer or truck limitations. You also may want to ensure you don't have so much battery weight that the balance of the trailer is significantly affected.
A quick trip to WalMart would probably provide the very same battery albeit under a different name, for alot less bucks...There are just a few actual manufacturers that produce alot of trade names...Spend about
$42 each and keep the rest for gas.
Installed 4 Trojan T125 into my arctic fox pd $88.00 each. I spent the last two weekends dry camping with my kids and the temp about 30-36 at night and the stat set @68 in the evenings and at 70 during the day with no problems. I do have a 100 watt solar panel but don't get much back this time of the year from it. Specs can be found at www.trojanbattery.com