Upon re-read,
"The other cable to the ATS comes from a 30-amp breaker in the main breaker panel. At the main breaker panel, the cable going to the ATS has positive terminated on the breaker outlet, neutral on the neutral bar, and ground on the ground bar."
Since your ATS switch receives it's A/C input from the main panel, your problem may be one of competing 'circular currents' causing the sensitive inverter GFI outlet to trip. Try powering the ATS from ahead of the main panel (where shore power first enters coach), not after (then divide entrance (in parallel) to main panel & ATS), and you should see a difference, problem corrected...
Best Regards,
3 tons
