welding will be pricey, this would probably work:
kind of hard to explain, get some 2 by 4's cut them into maybe 1 and a half or 2 foot sections, drill maybe 3 or 4 holes in two of the pieces in the same places, clamp the two pieces together on the middle part of the rail, slide carriage bolts through the holes you drilled, make them tight as fuck, you now would have a simple wood piece to frame supports out from.