I used 1/4 luan for the bodies and 3/16 s/s rod for the support.I drew up templates on card board and cut them out,then placed the cutouts on the luan and traced it.
Used a sabre saw to cut out the silos and just kept going till I ran out of luan,wound up with 6 dozen when that was done.I think that was 2 1/2 sheets all together.
To attach the rods I cut a 3/16 slot under the silo using an end mill but a roto zip bit will do the same.I used a drill press with a bolted on vise attached to it.The vise acted as a solid base to lay the silo on to give it stability while cutting the slot.The vise's jaws are open enough to allow the bit to drop inside them so the silo can be fed across the top of the jaws and cut the slot.This takes a little practice because the bit tends to "pull"the work to one side but you want it to go straight.Practice on scrap first.
I cut the slot about 3 ' into the silo.The rods are cut to 12 " and I belt sanded the end that goes into the ground to a point.The other end presses into the slot(they are they same size so it will be a little snug,which is what you want).
To install the rod first apply a little Ultimate glue to the slot and the rod end,then just press it into place.Because the fit is tight you should be able to hold the silo by the rod without it coming loose.This way you can put the silo aside while the glue dries and work on the next one(just don't lay them on top of each other or they stick together).
If you use coroplast,try heating the rod up before you push it in,it will melt into the plastic and make a tight seal on the rod.
For painting I just sanded the luan and used exterior latex primer and paint,walmart stuff nothing fancy.