Using one of the recently calculated tiles in the middle of the black forest (Lat48 Lon8, Lat49 Lon9), I created a Garmin map which contains, well, height lines :) . As a map which consists of height lines only is rather useless, I used sendmap to combine Carsten’s Garmin map with the srtm tile:
sendmap20 -l typ_gmapsupp.img srtm.img
Just copy the resulting file gmapsupp.img to the folder called Garmin of your GPSr and enjoy the height lines:
Unfortunately the height lines (which are in 40 meter increments) are labeled as either imperial or (more likely) United States Customary Units on the Garmin. I need to figure out whether this is an issue of mkgmap or a device setting.