Melnjoy, I know of two services in South Dakota, one in Florida, and one in Texas, that specialize in just what you want to do. We go through Alternative Resources (
www.alternativeresources.net) in Sioux Falls, SD. We took the weekly mail plan. We email or call (800 number or regular number) and tell them where to send it and on what day of the week. They send our mail Priority mail and it usually arrives in two business days. Twice in 18 months it has taken three days. We have it sent to the rv park we'll be in. I always ask the park if it's ok and verify the mail address. We've never been told 'no'. We did run across a park recently that had no mail service to their park. They probably had a box but wouldn't want to deal with the mail. So we had it sent to General Delivery at the local post office.
Hope this helps.