I use these people in Oregon and have for the past couple years - they are GREAT!!
HERE!
They also now offer a great email plan - they handle my snail mail and send out every Thursday and will hold or make special bulk forwarding when requested - a simple email to them telling them to hold or forward is all that they need. You send them money for postage and your balance is always on your mail label so you can see when to send them more money for your postage account.
I have packages sent to wherever I am going to be for a while, have yet to have a campground not be willing to receive something for me, I use Amazon a bunch and so far have had no problems.
Example - I was traveling for the past 45 days or so - sent an email to hold my mail and yesterday secured a short term PO Box at my summer job - emailed to have them begin to send my mail again - requested weekly. Will keep that going while here for the summer and then have them hold it again when I depart.
I have never had this mail service receive a package for me, as I don't want to incur the extra postage / shipping.
I have found these people to be very reliable and VERY easy to work with.
Good Luck,
Jim