hot gluing is probably a bad idea...
I don't know how hot the HDD is getting, but certainly I've seen HDD runs so hot that I've been burned by them...
you don't want a hdd drive attached by melted glue..
also hot glue isn't a very good thermal conductor, (or else the whole rod would melt in the glue gun)... so it's probably not the best way to attache this either.