I made a map using google earth and transferred it to the microsd by drag and drop. I put it into the garmin directory on the microsd card, where my waypoints get stored. Its a .kmz file named Japan.kmz. It is about 17mb. I can view it on basecamp, but it does not appear on my map list when I turn the device on. I tried to put it onto the device memory itself and it said it was too large, but when it's on the microsd, it simply doesn't seem to know it is there.
I also have a Japan map in .img version that basecamp reads from the microsd but the device doesn't pick it up.
Red90 - the custom maps don't appear on the map setup page, so I can't check this.