Did you have longer lasting batteries when you drove to the track the first night?
If you are able to run your vehicle engine for 30 minutes with generator off, then do the same time test and get different results you may just have bad connections from the generator to the house batteries.
You should have a multimeter and measure your voltage at the coach batteries with nothing running, then with the generator running, then with the engine running and give us more information.
There really is a lot that can be figured out before you start spending money. The sad thing is, changing out good parts usually results in tight connections when all that was needed was a loose connection needed to be tightened.
