Thanx all for the ideas. I'll give the peppermint oil a try for sure. I also found a site that sold spray foam that contained rodent repellent (Cayenne, spices) that they said coupled with the use of Copper wool would block out the rodents along with unwanted air leakage. it was IPF PUR Foam, i think.
I've been thinking on the use of either steel or copper wool, too. The copper doesn't rust is it's only benefit over the steel. I can also install some sheet metal plates over the holes and foam inside the cavity.
BTW, the Botanical Repellent I've been using is "Fresh Cab Botanical Rodent Repellent", and up to now has been pretty effective.
I'll start working all these things together and see how it goes.
2016 Thor Hurricane 29M