RE: Sites for gas setup advice.
One of the reasons for the dual battery leads is to lessen the current load thru the small wires/connectors we use in our rx systems. They are supposedly good for 3-5A continous, with short bursts beyond that. You can plug a battery(or two) into any spare port on a receiver. The batt share by SmartFly, or the Wolverine switch, are intended to use two batteries, and provide a layer of safety if one battery should fail. They keep the circuits divided between the batts, so a dead one doesn't draw down the other, and you still have power to your rx. If you're not using 2 batts, then there's no need for the batt share.
As far as running one lead from a single battery to the rx, and a second lead from the same battery to the ignition, I believe it has been done, but that opens the possibility of interference. The optically isolated kill switches are supposed to prevent that. Personally, I wouldn't do it that way. I would use either the TechAero BEC or the RCEXL bec kill switches...