It's not that hard to imagine that if it's been setting in the NW, unused, on a dealer's lot... that there's a bit of mold here and there. Not in the walls but
in the window tracks or on the glass itself.
Damp Rid sells a mold & mildew spray. There's a blocker and there's a stain remover. the difference is one has a blue spray nozzle and the other has a red spay nozzle. I've only seen it for sale in the Lowe's in Longview, WA. I use it all the time. Safe on skin. Safe on fabrics. Does not need to be rinsed.
You can probably get it online. you can spray the RV yourself. Best to spray it around the inside before you start to put anything into it.