I,m thinking the U/C wire legs will need to be able to flex inside the spats for landings, a little. So after re inforcing the insides of the spats with extra glass, i think plumbers type pipe insulation packed inside the legs will allow some movement, but will also give some cushioning effect, i.e. not directly transfer the side loads on a less than perfect landing directly to the spats.
re. the spat bracing wires, i,m going to attach them THROUGH the spats, directly to the wire legs & include some small, but strongish springs, in the attachments to allow a little give.