Some time ago I have read in a forum that users had drilled a small
hole in the foot of the dome in order to let condensed water pass.

Furuno's radar antennas that I have seen already had small hole and pipe in
the bottom. Displays also. According to my experiance, if you strictly
follow instalation instructions there must not be any problems. I don't
recomend drilling a hole. If there is a hole, leave it, if there is not,
don't make it. The only hole I recommend to make is in the dome mast, so
that mentioned flexibile pipe can "pee" through that hole. So, 4 holes for
bolts, 1 hole for cable and 1 for that tiny pipe (if there is a pipe).