Sorry, can't help with a recommendation for them. We used the Escapees RV Club's successfully for approx. 18 years.
I will say that if you're looking for a permanent address such as for full-time RVing, there are things you need to keep in mind. First you have to pick a place of domicile. Then it's advisable to have your address, driver's license, registrations, voter's registration all using the same address. In addition, your medical and vehicle insurance rates/plans will be based on the mailing address you use.
Good luck! It's a big decision to make.
If you're just getting a forwarding address for short-term use you have options.
Full-timed for 16 Years . . . Back in S&B Again
Traveled 8 yr in a 2004 Newmar Dutch Star 40' Diesel
& 8 yr in a 33' Travel Supreme 5th wheel