When we use to move around a lot (it's been about four years ago, so things may have changed) I did the following.
- Move everything you can think of to online banking, and e-mail notification;
- Go to the PO and tell them you will be on the road and would like to put your mail on hold (and tell them the following);
- When you want your mail pick a park that you plan on being at about a week out;
- Call the park and ask if you can have mail sent there;
- Call the PO and tell them the address of the Park you want the bundle sent too;
- A week later show up at the park and wait for the mail if it isn't there.
The above can also work with "general delivery" to an on route PO. With that option if you have to hit the road prior to getting the mail you can have them send the bundle back to the original PO for another attempt.