Gav, Welcome to the forum.
Our 4G RADAR
dome is mounted as you describe; on our Mizzen mast just below the spreaders.
I assume it is about the same size as the 3G, but don't know for sure. It doesn't weigh much.
We were lucky in that the old RAdome platform worked for the 4G dome [after we drilled the new mounting hole pattern.]
It works well from this position. The one exception is we get an errant shadow ostensibly from the main mast typically appearing as a bogie about a mile ahead of the boat— always dead in line, and it doesn't stay visible. With your wood masts you may not have this same experience.
Does this cover what you were asking about?