www.myrvmail.com in Crestview FL. We used them for a year and they were great. They have different levels of service. Their top service will scan your mail then shred it or forward. You can read the mail online. They have lots of info on their website.
For temporary (not full timers) mail forwarding I would use UPS. We have used them for several packages with no problems. Right now our daughter collects our mail and we provide an address for her to forward about once a month. Of course we have online and auto bill paying so our mail isn't all that urgent. We buy postage paid envelopes and small boxes from the post office for her to use so she doesn't have to pay the postage.