In most of the previous Garmin models .img files had to be in a folder named Map.
Only certain filenames, like gmapsupp.img, were recognised in the Garmin folder.
Now it seems it doesn't matter if they're in the Garmin or Map folder, you can name them what you like: tested on 34xx, probably it works on Etrex 20/30 too.

My 34xx, the gmapprom.img and a non gmapsupp.img

kq3ow

bessk7