Base plates are simply the licensing state that you get you plates from. An example is like for me my base plate is from Ohio (cause thats where I live) and when I register for the plate I can add or subtract states from the plates depending on where I want to run. The cost of the base plates depend on how many states you register for and how many miles you run in each. Some carriers actually get thier own base plates from a different state then what they are headquartered in depending on the costs.
How would one be able to do this? I'm a assuming a mail forwarding service to have an actual address to register with in a precipitating state allows non resident registrations?