We are now in our sixth year of fulltiming and I'll split the difference on the previous responses - our first coach was acquired while we still owned a home, no problems, and we took the loan interest off our taxes, along with the conventional home interest. Totally legal. However, the concept of living in the coach full time, although we did because our home was leased out, was never discussed with anyone.
Our second coach was acquired after we sold that home, and we had several potential loan suitors who could not get the concept of us not at a residential street address. We subsequently financed the coach with our bank of many years without further ado. My banker, however, knew exactly what we were doing because she knew our situation but it was never pointedly discussed.
Since 9-11, and as a result of some interesting banking events, it has become very important to some people to know exactly where you are to be found should they come looking. We have had no issues as Escapees with permanent mailing address in Texas, ever.
The debate over debt and what you should or should not finance is extremely personal and not any of our business, and full timing has no bearing on what you decide to do with your money. Different situations demand different solutions.
My advice is to work with your lender, you cannot predict what will happen after the loan is made (maybe you full time, maybe not) and he does not really care. If you meet the underwriting criteria on the day of the loan, that's the best the banker can hope for.
Do your homework, evaluate your options, and proceed with the best plan you can make! Best of luck!
Kim