This has been an ongoing process for us since we started fulltiming. We are often in a travel mode where we don't know where we will be very far into the future. Our fallback mode is to have everything sent to our Escapees mailing address in Livingston, TX. They will accept most things from USPS, UPS, FedEx, etc. and notify us of new mail and packages. We will usually have them forward stuff via USPS Priority Mail to General Delivery in a town we will be staying near. We try to avoid using post offices in big cities and very small towns. Since Priority Mail is usually 2-3 days, we can make this work with our travel plans. The biggest downside, is the extra shipping cost and time delay, especially since companies like Amazon now tend to use fixed box sizes and often ship in larger boxes than needed. Escapees will not open packages to repack for shipping (understandably), so must pack these boxes in even larger boxes or re-ship the original box. Be sure you know the General Delivery rules in a particular area. In many cities, only one post office handles general delivery.
When we have a reservation at a regular campground or if we will be staying a while, we will check with them if they will accept packages from various carriers and most will. We will then have things shipped directly to us in care of that campground.
Art