You should only use 1 fuse closest to the batery. Summit sells 2 gauge batery relocation kits that are junk! Its not even thin strand! Sold that crap to a honda ricer after it killed a optima batery and my car never wanted to start with out a jump!
OP is right 0 guage amp wire is your best bet. I was going to get some off egay but it went up from 50 to $75 for 50 feet of 0 guage amp wire. Its not a good deal at a auto part store, BET! Now I just run a miata batery to clear the intercooler piping and never had a problem.