Thought I'd give a little more detail about the motorhome batteries that I wanted to get.
When we bought Sherman, he had two old "group 27" 12v batteries that are used to power the house part of the motorhome. There is a separate battery that is used for the engine.
The house batteries are used for lights in the evening, power for the inverter which supplies 120v to the laptops, and power for the electronics for the refrigerator (the actual cooling is done by propane).
We replaced the old "group 27" 12v batteries with two new ones from Walmart in late December, 2007. When using the house batteries, the only way to recharge them is by driving, or by plugging into 120v, or by running the onboard generator (which is noisy and uses gasoline). Or, with solar panels. We quickly found out during our first trip to Mexico that we needed solar panels.
So two 80 watt solar panels were purchased in September of 2008, and our electrical needs were pretty well met during our second trip to Mexico in the winter of 2008-2009.
But we always had to be cautious about our use, and a couple of cloudy days in a row were enough to make us worry about not having enough electricity. I always thought the perfect system for us would involve one more solar panel, and more battery capacity.
So I bought one more solar panel off ebay.
The batteries we had were cheap Walmart "marine" batteries. These are not true deep cycle batteries, and you have to be careful that you don't discharge them beyond 50% because the battery life will be severely shortened. I wanted 6v golf cart batteries. These are true deep cycle batteries, specifically made to be drawn down, and recharged again. And they have way more amp hour capacity than "group 27" marine batteries.
From everything I've read, the very best value for the dollar is with Trojan brand T-105 series 6v batteries. The very cheapest place to buy them on the whole continent is in Florida. Just so happens that the best price dealer is just north of Fort Myers, and that's where we went to buy four of them. We paid $87 each, and a core charge of $16 each because I didn't want to leave my old batteries behind just yet. These batteries cost upwards of $165 each in Canada.
So now I just have to install them, and the new solar panel...and we will have power to spare! In fact, even with a week of cloudy days, we will likely still have enough power for our basic needs. And really, would not ever need to plug into 120v electric again. Truely self sufficient.