Maps not appearing in Base Camp

The version of OSM that appears the best for me is one I found on Gmaptool: http://www.gmaptool.eu/en/content/usa-northeast-osm-topo-routable
I downloaded the compressed file: US_Northeast_OSM_Topo_v26.7z
and extracted using 7zip as recommended. BaseMap could not find the unzipped file (folder). I saved the unzipped folder in a new folder I created in my documents : as US_Northeast_OSM_Topo.gmap
How do I get this into maps on Base Camp and then transfer it to my device, an Oregon 750?
I am very new to this and just feeling my way.
Thanks