Although I haven't heard of this issue with RV's, it is probably related to the housing market and resulted from what is called, "Buy and Bail." In the housing market there were many people who became upside down in their homes when the bubble burst, but they had not lost their jobs and still had good credit and could afford the house payments. So what they would do is go out and buy second homes and move into them, and then just bailout on the first house and let it get foreclosed on. So the banks came up with rules to try and prevent this. My guess is the same thing has happened in the motorhome market.
In your situation, why wouldn't you just take an equity loan on the house and buy your second motorhome? I know some people don't want to risk the house, but in your financial condition as you described doesn't sound like that's an issue and you can get a better mortgage rate on a house versus a used motorhome.