Unfortunately I just noticed another inconvenience. My primary area of interest is right along a UTM zone boundary. I had hoped that the tiled export would treat tiles from each zone separately when downloading them (in spite of the fact that this is not done during display on the screen), but instead I end up with a large number of blank tiles (using Topo 4 m). Even if it would just leave off tiles on the other side of the zone boundary when creating the KMZ file, at least that way I would not be wasting tiles toward the 100 tile Garmin limit. I would consider using MyTopo, but that only comes in one (2 m?) resolution for tiling which would significantly decrease my potential area to work with. It looks like the only work-around is to zoom into a smaller area that goes right up to the zone boundary, exporting to two separate files from each side while making sure that the total tiles of both add up to less than 100. I suspect there might still be somewhat strange looking results when the two custom maps are both activated on the GPS. By the way I considered the TopoWMS maps also, but they don't show up in the KMZ tiling options either.
