I wouldn't tell them. Most RVs are built with materials that stand up to average use, but full-timing is really hard on an RV. I did it for three years and I pretty much beat up two travel trailers in the process.
They're worried about their investment. If you full time in it for three years and destroy it, then quit making payments and they reposess it, they're left with a spent vehicle and they won't recoup their losses when they sell it.
If they ask if you're going to full-time in it as part of the application process, it would be illegal to lie, but its not a lie if you actually go away from it for a while. Let's say you're parked in FL and you fly home for a couple weeks when your new grandson is born. Technically you aren't living in it full-time