How do you typically mount and build a flat tank for the double bar cwc bicycle? I am talking about the kind that is just a flat piece of steel etc. to fill the space
Start by making a cardboard template, trace that onto whatever material you choose to make the plate out of, I've been using old street signs, to attach it you can weld tabs to the frame, use metal straps like this stuff
or I've seen guys use copper, I usually use these cable clamps
they come in different sizes, here's a poor quality pic of one I made last year
if you poke around in the "show me your..." forum there's a thread on this stuff, it's where I got all these ideas