MAC,
I've never removed them, not sure why you would want to. I do take the battery out of the boat; in the event it would ever freeze and crack I don't want electrolite in the bilge. The Montana has a catch tray to catch a spill if it freezes. The batteries shouldn't freeze if you have any level of charge on them.
We just take our antifreeze with us in the winter. We winterize & drain the tanks before we head home.
PS - just ordered a new marine dual battery tray per Mike's (MAMalody) suggestion under Battery Power post
http://www.bluesea.com/product.asp?P...62&l1=7462&l2=. It is designed to catch the entire contents of both batteries I believe. Next spring it gets the CW golf cart batteries.