I used a 60 amp contact block vice an SSR. Next time I will use two 30 amp. Cheaper and I minimize the #6 wire. Than stuff is tough to bend around in a box.
http://stores.ebay.com/English-Wheeling-Machines its there.
You see where my fan is? I don't think ducting top to bottom is neccesary and I consider the fan for convection rather than heat destratification (for lack of a better term)
ie I am not trying to even out the temp top to bottom, that takes care of itself, I am trying to get the air that is nearest the powder coated object to circulate.
Gene