You are definitely on the right track. When you choose your power inverter consider the following: buy the inverter for around 40% more of your anticiapted load. You will need a double pole transfer switch to isolate the inverter from the generator(and visa versa). A simple double throw double pole switch with fuse or breaker protection should do it. You wouldn't necessarily have to isolate the curbside circuit as the double pole double throw switch would simply be switching the power from the existing generator to your new inverter for only the roadside circuit; i.e. you don't need to worry about the curbside power source as it will always be connected to the other branch circuit. Even if your generator or other source came on the system would be protected no matter what the the roadside configuration was set to as only one source of the 2 roadside power sources would be connected at any give time to the roadside circuit. The six dots represent the connecions for the double pole, double throw switch; shown supplying the new inverter to the roadside circuit while the source from the existing generator or inverter is disconnected via this switch from the roadside circuit:

existing * *------* new power inverter; switched to source
* *------*
^
Middle 2 dots represent your roadside circuit and represent the "throw arm" of the switch. Safe and simple! If you don't have a voltage meter for your batteries you can purchase one for a few bucks. Just run it across the terminals so you will know battery condition as it is being drained (you may already have this indicator) You can find a transfer switch at an electrical supply place, maybe even Lowes. Make sure you get the switch that will be in a protected enclosre. The enclosurre can be purchased seperately if you can't find the switch/enclosure package together.

Good luck....gary