Thanks for your reply.
@ Joe
Honestly I would prefer 2 m FM from such a point, but …
I used 2 m FM during many activations in the past, but with only a very small success, unfortunately. So my main choice is SW, also on summits witch such towers.
@ Andrew
Yes I know my “vertical” is more a dipole, one side vertical and one horizontal near ground. Its a little bit similar to a sloping dipole but with 90…100° in the feeding point. On the tower I used my antenna like a quadrant antenna but with one wire close to the platform and maybe close to much metal. I am not sure about the construction below the wooden surface. Insofar as I remember the settings of my ATU were not so different from those with the antenna mounted on ground. Maybe there are not so large metal parts. I am now curious about the radiation diagram respective to much metal or nearly no metal in the Platform. In the next days I will simulate this.
@ Armin
I was thinking about a wire from the tower down to a point near the ground. During my both activations every time people where around the tower, on the staircase and / or on the platform. I was looking for a simple way to use the tower and interfere with them as little as possible. My solution seems to be usable and I was curious about the results with this version.
@ Michael
Good to know about your experiences.
I do not care too much about this 
. On many summits I was using my 20 m dipole (with asymmetrical feeding) with good or enough success, also on flat summits and surrounded by many trees or close to a lookout made from iron.
