Dual/Backup Battery+Combiner Wiring

I'm an auto electric newbie about to start a project on my truck. I've researched online and believe I have a handle on most things I plan to do, but I still have alot of questions about wiring capacities and fusing requirements of the starter power components. I plan to install a 1200W AC-to-DC modified sine wave power inverter in the way back of my truck. I'm choosing this location because there is no good location to mount it any farther forward without it being enclosed or covered and I'm very aprehensive to run an inverter where I can't get to it in an overheat situation if it's built in protection fails...I was in a car where an inverter with over voltage and over temp protection burned resulting in a scary situation. The shortest route from engine compartment to the back is ~15'. Everything I've seen indicates that you shouldn't run an inverter this far from the battery unless you have a pure sine wave inverter which I do not. Now I also plan to add a high volume air compressor in back that pulls 60A at times. Plus I've also wanted to install a backup battery. So I figured if I mount my backup battery in back, I can power the inverter and compressor directly from it with shorter cables. Plus in a pinch I can use the second battery as a starter backup. So here's what I want to do: - Install something like an Optima yellow top in back up under the body. - Wire a fused distribution block right off of this batter - Ground the second battery and inverter to frame To charge the battery: - Use a battery combiner like this 250A Xantrex Pathmaker to charge the main battery and the backup battery and still allow me to run/start off of the second battery. This is just a fancy voltage sensing relay with some adjustability and ability to connect the two batteries, no? - Run the existing cable from the starter/alternator into the main terminal of the combiner - Run a new cable from that same terminal to the main battery - Run heavy wire from the second bank terminal of the combiner to the second battery's positive terminal My questions are: 1) will that Pathmaker combiner's solenoid with a 250A load limit beable to support the draw from during a start? 2) what gauge wire should I use for the combiner to main battery? 3) what gauge wire should I use for the combiner to second battery? 4) which of these extra cable runs needs fusing? It seems that the new wire from the combiner to the main battery needs fusing to protect it during start. And wouldn't the long run from the front to back need to be fused at both ends at the front of the truck to protect from a short during recharge of the back battery and at the back to protect against a short during start? Or am I thoroughly misunderstanding when to fuse? 5) what recommendations do you have for grounding to frame in an area where there are no grounding blocks? Perhaps, you know of a good book that I can buy to help me through this? I don't plan on doing any security system or audio system work, so something that really just deals with basic power distribution and non-audio accessories would be nice. '03 Hummer H2

I did a little more research and answered quesiton #1. Specs on the combiner are 250 A: 250 A continuous, 1200 A peak Anthing pointers questions 2-4 would be great. I just haven't been able to find any useful info on long cable runs for starter circuits.