I work for the Texas Dept. of Transportation.... we pour concrete test beams at each concrete pour....we pour extra beams each pour... there are beams that are not breaken and the contractor has to haul them off.... they will give you all they got just for the asking.... Cheap enough
They are 6"x6"x20" and weigh 55# each....one on each end of your beds should sink it no problem.....
Hope this helps.... wish you had them beds down here... they sure would come in handy....
Good fishing.........