Try this one.
Unpack it into the "deltas" folder"
The Ft Drum base map, is one that is shipped with the original intsallation of SB, so you should find the folder
File path is whatever you choose in your installation then:
Steelbeastsmaps\Ft_Drum_10m [autocreated base]\deltas
you extract the rar file directly into the "deltas" folder
FT DRUM NY 50km (edited)_10m.rar