I'd like to see your solution to adjusting the aerial to different signal sources; we've been to many sites where the best views / level ground would requires parking our bongo in a specific direction.
Neat job so far ...
Underground, Overground, Bongoling Free, the Bonglers of Bedford, common are we ...
Having given it considerable thought for a good 30 seconds or so the solution was easy. Just flipped the bracket through 90 degrees and used the aluminium tube with a 90 degree bend in it that was supplied with the aerial. You can reach out to adjust the aerial so even if its raining your fine and it turns through 360 just above the free top.
Measurements are not important now with the bracket towards the back of the black reinforcing alloy bar. With the bracket in this location it comes down in a part of the free top with enough space to comfortable take it. The bracket and alloy pole all come with the aerial so all you need are the two bolts to fix the bracket and a drill to make the holes.