In a strange sort of way, I think you're so-called expert may be on to something with the sun concerns. It isn't about the radio waves, however. Ever notice how the tin nailed to the sides of the elevators is all short pieces? Kinda like they used scraps from a previous project. That begs the question of; where are the elevators with full length tin? I've never seen any, have you? The characteristic of a cribbed elevator is to shrink and expand depending on how full the sections are and the moisture of the grain that's in each crib. Add in the effects of sun warming and swelling the east side in the morning and progressing to the south and west while the north remains relatively cool and you will have the top moving more than you may want, when an inch is too much. Looks like that elevator is still used also. Ever been up at the top when a fully loaded train comes by? That makes it sway also. Might make for some real interesting reactions in an auto steer tractor if the RTK base is moving a couple inches as you're driving down the field. The shuttle facility at Macon is a concrete slip formed house that's 135' tall. Near the man-lift and leg, there is a length of wire suspended from the top that has a 2' section of steel rod attached at the bottom (a giant plumb bob of sorts). There is a small cross painted on the floor and a red circle about a foot in diameter that's painted around the cross. Very seldom does that plumb bob stay exactly on the cross. When a train passes, it moves several inches!

All this leaves me wondering why you're fixated on involving the elevator at all? One thing I've noticed about elevators is that they're always located by train tracks. One thing I've noticed about train tracks is that they're seldom located on the highest ground. Couldn't you move a mile or so towards the hills you talk of and actually be higher standing on the ground than you would be at the top of the elevator? I think a stable 6 foot tripod mounting the RTK globe and a shorter, thin antenna structure to mount the transmitter all out in the open where you didn't need to worry about signals bouncing off large steel structures would be a much better solution.