30-40 RV's..... my adivce is stay away.
You want to detail that many RV's. I hate it when i have to do a ford expedition or excursion. I have done RV's in the past. Interior and Exterior. I felt more like a house keeper then a detailer.
If that will be your only detailing, then it might be ok, but to take on side work on top of detailing 30-40 RV's, you may end up hurting yourself businesswise.
You will be so tied up with detailing rv's you will not have anytime to detail othe cars, or will be to tired to detail them.
this is just my thoughts..... but
if you were to approach them here is what i would do.
speak with the mngr in the place, explain to him how you can be of service and explain how he will benefit from hiring you. Think of ever question he can possibly ask you before you go. You dont want to answer questions with hmmmmm,, uhhhhhh. Answer quickly and confident. It makes you and your company look better.
You may also need to have insurance to work on the cars as well.