Hey Jones - I don't have my 80 anymore, nor am I local, but I can tell you that William and I did similar setups on the cheap.
I got welding cable from:
Pacific Welding Supplies LLC
2902 South M Street
Tacoma, WA 98409
(253) 572-5302
They were cool and cut me the length that I wanted.
I grabbed a battery tray out of a 91 or 92 FJ80 from the pick and pull for $10.
I put some ends on the welding cable, and ran my batteries in parallel (without an isolator).
Isolators are easy to add later. I was looking at isolators on amazon and really liked the Blue Sea setups. Here's one with a switch for the dash:
http://www.amazon.com/Blue-Sea-Syst...576&sr=8-5&keywords=blue+sea+battery+isolator
They are cheaper without the remote switch, but I liked the idea of having something in the cabin.
Once I had two batteries hooked to each other, I had no issue running the fridge for a day and starting afterwards. I would have added an isolator eventually, but it wasn't a big deal to me.
As always, proceed at your own risk.