how to make a waterproof seal bimini top to radar arch

[lime4x4]

Below is a pic of my radar arch.I've decided that i want to have the bimini tops attach to the radar arch so that i don't loose my lighting in my arch

here is link to the radar arch pic

http://picasaweb.google.com/lime4x4/Lunasea#5380949331830253762