Janila, you are a letterboxer after my own heart :). I do the same thing. My husband and I are often dreaming about the next trip we are going to take, so I begin customizing addresses already at that time. I've found many boxes I wouldn't have found if I didn't customize it.

I even go a step further. I search for boxes that are only listed by the state. Here is what I mean:
I do an AREA SEARCH under SIMPLE SEARCH. Under REGION, I'll go to the state I'm looking for. For example, I'll type in MICHIGAN. Once I've done that, all the Michigan boxes I haven't found are listed. But then I will EDIT SEARCH. I will change the DIST (MI) to 0 and run the search again. All the boxes listed with simply the Michigan location will come up and I'll have access to several other letterboxes. I then customize those locations and, hopefully, find those letterboxes while on my travels.

These letterboxes are often mystery boxes and are well worth the time and effort it takes to figure out the location and solve the cipher/puzzle if there is one.

We do the same, I have alerts set up for Michigan to send an email.
The other locations I track, Rhode Island, Maryland, Grand Haven, MI I have set up as a widget on my menu!