First I cut off the tops of the towers.
Next I cut a small strip of styrene to join the lower towers. The glue joint on the upper tower of the previous version was pretty weak, so I drilled and pinned it with a brass wire.
I drilled two holes on the underside to give more glue surface.......
..........while allowing me leeway to set the platform level.
If it turns out I don't like this arrangement, I'll abandon the two-tower concept and go back to a single tower. So far I'm OK with this set-up, but who knows how I'll feel in the morning. Your comments always welcome. Don