[bojan]

This is the situation I am talking about.
Of course, the residual amount of pressure will be dependent on bolts and how tight they are.
Also, when scope is pointing upwards (towards zenith is the extreme case), half of the channel is under compression, the other half is pulled apart.

Anyway... I found the suitable piece of 20x20x3 channel in my shed.. so tomorrow I am putting the whole thing together.