A comment about Costco batteries;
I've been screwing around with either sets of two 6 volt batteries, or now I have 4 6 volt Costco batteries. Costco is a great company to work with, they are everywhere, and have good quality products. HOWEVER!!!! The 6 volt batteries just don't hold up all that well.
We just pulled into town from a 4 week trip where we experienced extreme weather changes. For what it's worth, we charged the batteries with a PD Wildcat to 14.4 volts and about an hour later, the volts were down to under 13---no usage from us except for the propane refer. 3 hours later, the readings were 12.5 with a couple LED lights. The heater ran some in the night and by morning, the volts were right at 12 even. These batteries were installed new in March. The reason these batteries were new, is two of the other Costco batteries failed and the store had me replace all of them.
When these are to be replaced, I'm going to explore Trojan 125s.