Billy, it's 3/4 emt. The space between tubes is 16" for an overall width of 40". My seating setup revolves around these "runners" and some lo-pro type fittings I've had to come up with (cause nobody makes any). The runners going from the front frame section to the second will rest on the lower frame cross-sections, and will hold the ice chest. The runners going from frame 2 to frame three will be resting on the upper cross sections. Gonna strap a drybag to those and use it as a seat with my knees on the tubes or feet down by the icechest. If I need to, I can lower my runners to the lower cross members to reduce my ride height by a couple inches, but it also gets me closer to the water. I went 5" wider than stock with the idea that the extra width will help counteract a higher center of gravity. Guys I run with ride this way on their Sotar duckies with pretty good results.
The paddle I run is the old school Carlisle (don't know what the actual model number is). Am also thinking of running a single end canoe paddle. (?)