We are trying to figure out a way to get all the way points off of our GPS 45 so that we can put them on our new GPSmap 60CSx. Base Camp only seems to recognize USB based GPS devices. The GPS 45 we have only comes with a serial cable connection.
I use a serial cable with my old GPSMAP76S and Mapsource connects with it just fine. You might need some special serial cable drivers for BaseCamp or just use MapSource.