Dirtsailor 2003: Had to make some changes to first mock-up. Did take your advice & installed HardiBacker on the floor & on all 3 sides under the flashing sheet metal.
Am now going through the seasoning process. Washed cast iron skillet & let dry. Ran all interior parts through the dishwasher, used a power washer with Simple Green on the exterior box. Let everything dry overnight.
Just before seasoning, attached exterior to cart & installed all interior grates. Installed felt oven gasket material on outside where doors meets box. 10" cast iron skillet rests on fireplace bricks. Sprayed all inside with canola oil cooking spray. Attached feeder hose, ball valve, & supply hose, then tested for leaks.
Fired up smoker full tilt [all valves wide open] with wood chips in skillet. Got temperature up to 380, staying between 350 & 380 for almost an hour. Everyone is right about chips - don't last very long. Unit seemed fairly airtight, only "loose" smoke I could find was through the holes for the thermometer leads, & a couple of tiny tendrils at the upper corners of the top door.
All throughout the seasoning process, all the metal sides were cool to the touch whereas the top red trim got warm. Am seriously thinking about installing some more metal drip edging around the red trim.
Have ordered the Master Forge stainless chimney. Will install it on the top middle & seal off the back vent.
Will start off smoking something simple to see just what it & I can do. Have to get my act together, as Mama has strongly hinted about me smoking the Thanksgiving turkey.