There is no reason, based on what you have told me, why the bank should be linking the mortgage to the motorhome loan. Each loan is a separate contract, a separate obligation, and has its own security.
However, that being said, it is possible that the loan on the motor home has a provision saying that if anything happens that impairs the security on the loan (including your personal bankruptcy), they can demand full payment. The bank may be interpreting the foreclosure on your house as being a threat to their security on the motorhome loan. But if you are current on your motor home loan payments, the bank should not be able to call in the loan.
The position you should take wth the bank is to ask them, "Show me where in the motor home loan it says you can accelerate payments if I am not in default."
Lawyer
26 years litigating important insurance and injury cases; well-known legal author