At Club Car:
Battery bracket Check for fitment. Farmboy may have the easiest solution. Aluminum angle and threaded rod, nuts, and washers are all sold at Home Depot or other big box stores.
The footprint of a GC2 6V is really close to a BCI grp 24 12V. With a bit of tweaking that might be a straight installation. If brackets or clamps are difficult to acquire or difficult to install, there are other ways of securing batteries. A bungy cord has worked for me, many times. It may not hold up to a vertical attitude if the trailer flips but I'll have other considerations if that happens.
๐You'll get the best battery longevity, IMO, by being diligent with maintenance and limiting the draw to 50% of the total capacity. Also, periodic or float charging is the best for any FLA battery. When charge power is not present, the battery is sulfating. 6V golf cart batteries are the best for drawing down frequently and have good durability. 6V batteries, if you don't already know, love to get around 14.8 VDC-15 VDC, when charging. Some of the RV converters don't deliver that. An easy work around is to put a small battery charger on the batteries, occasionaly. The most elegant solution is to replace a lesser converter with one of the Progresive Dynamics converters that does offer those higher voltages. A solar charging system with a charge setpoint that is adjustable will do the trick, too.
Good luck with the new batteries.