Messages

Can anyone help me with loading map files ending in .gmap into Basecamp on my MAC.  I was able to load .kmz files with no problem, but no luck with this other format, even though providers claim they are for MACs.  They do show up in the Map Manager, but when I try to import them into Basecamp, they show up as greyed out. I've spent many hours on the Internet trying to figure this out with no luck at all. Any help is appreciated. I have the latest version of Basecamp installed.