I think Boatdoc pretty much answered your original question, along with the price consideration.
There are lots of things to consider AFTER you install your battery: How long you will be camping, with or without 115 volt connection, how many lights/appliances you use, etc.
The website below has a lot of great information on batteries, the 12 volt
system, etc. There is a part two (Look for link at bottom page 1) that covers solar, energy saving suggestions and a whole lot more. Super site IMHO for easy to understand 12 volt
info, all layed out under headings for different subjects. Check it out.