??--"Hot" and "Ground" Wires to Batteries

[Montana_2694]

Our Montana is in storage and I can not easily get to it:

I bought a Blue Sea Battery box for my two 6v batteries in which I run in a series.
http://www.bluesea.com/product.asp?P...62&l1=7462&l2=

Previously, I had the batteries just hanging out, bungee corded together but finally got around to addressing it after reading a post about the issue and PM’ing Padredw.
http://www.montanaowners.com/forums/...ead.php?t=6579

I figure I will need to lengthen the red wire to make it work right; maybe the white one too. What gauge, type should I being looking for and which place will I be most successful in picking it up?

Thanks!