I am going to change my mind about epoxy bonding aluminum.

I just went through a similar issue, 3000 psi bond of 2 aluminum sheets. To get a reliable bond you need to sand, 2 part etch and then use a pressure and temperature cure epoxy. The curing requires the 2 plates to be pressed together at 5 psi or more and cured at 250F. A no pressure room temp cure will have a lot lower bond strength, 100 psi(?). The larger gap of a no pressure cure also makes the bond easier to break (don't ask me how I know).

The reason we have gotten away with this in the past, is the loads are mostly compression and if the fit at the joints is good, most of the load is taken up mechanically. Just as a guess, to handle the load with bond only, you will need about 200 sq inches in each mast segment. Consider the 3rd segment as just a spacer.

If I ever have to do this again, I am going to use epoxy and add a couple of monel rivets