So I was told I can replace the two 12 volt batteries on my horse trailer with two 6 volt batteries and that would keep the LQ lasting longer when on battery power.  Does this sound like a good plan?  My husband does  a lot of primitive camping and has lost the furnace blower after a couple nights with no plug in power.

Yes... (2) 6 volt batteries in place of  (2) 12 volt batteries is a good change.  BUT ... the main reason to do this is avoiding having batteries in parallel.  When batteries are in parallel, they cause self discharge if there is any imbalance.  That is the stronger battery charges the weaker battery.  Then the former weak battery charges the former strong battery.  6 volt batteries are connected in series so they don't affect each other. 

The golf cart batteries may be larger than your existing batteries.  In that case you WILL have more energy to run stuff.

I think it is a good idea when you can fit 4 of the 6volt batteries. That way you still have 2 12volt banks. With 2 12 volt batteries If you loose a battery it is no big deal you still will have 12 volts but the system will go dead quite quickly. If you are running 2 of the 6 volt batteries and you loose one "goes bad" you are totally dead. No power at all. I dont know about you but with my luck it is too big a risk.

Lee