Adrian,
It really isn't going to make all that much difference.
Run the feed line as best you can, see what the 'problems'
are and then try to minimize them. Needless to say, at 20
feet height, on 80 meters, how you run the feed line isn't
one of the 'biggies' to worry about. That's not to say that
you shouldn't do it as 'correctly' as possible, just don't
loose a lot of sleep over it.
'Doc