Since you're going to two different places within two months, I would recommend you have your post office forward your mail only one time and do so at the end of your first month stay to your second place and wait until you get home to view the rest. Do your really receive that much mail anymore? You are very likely to have some kind of mix-up if you try for each park within a three week block of time (excluding getting there; leaving; moving to another spot and leaving). That doesn't leave much time to wait around in case there's a mishap.
The very best is to have a neighbor or relative gather your mail daily and they can send your important-looking mail via Priority Mail to the local post office care of General Delivery. It'll get there in 3-4 days. Just make sure the post office is in a small town as bigger towns have multiple post offices and certain ones only accept general delivery.
Or...have them send it directly to your RV park but check first that they will accept it. Some do; some don't.
General Delivery is very safe and efficient. We've done it for 16 years of full-timing without any problems - all over the country, including Alaska.