RE: Leaving our dog in the trailer...
A suggestion might be to 'leave' and spend some time at the site next to yours and see if Fido really doesn't bother other campers. Chances are he does and you have no idea. Or, ask your neighbor to be honest with you. I'd bet they bark way more than you think they do.
RE: Leaving our dog in the trailer...
Michigan State Parks consider pets left in the RV as 'unattended' and no different as anything other pet tied up outside.
http://michigan.gov/dnr/0,4570,7-153-10365_10883-31329--,00.html