So, 10 hours of gen time plus running the coach engine... all to charge a couple of batts? I'd hate to have those gas bills, not to mention the wear and tear on both the gennie and coach engine.
And what if the OP stayed at a campground? He'd have no other choice but to pay for hook-ups... no 10 hour charge times there. So, two weeks camping at the extra cost for hook-ups, at say only $10/ day... that's $140, the same as a new charger. At an extra $1500 for a season, that's an entirely new 12v charging/ electrical system, including new batts, and solar.