Frame builder's special - complete hatch, w/Riverworks drop bag (11-13" deep, 20" wide and 48" long) and 1/2"HDPE floor, 1/8" diamond plate ("DP") hatch cover, stainless steel piano hinge and latches (Southco, $45 apiece). Fits 48" interior width (C to C of side tubes), creates 22 inch wide bay. Overall opening is 44 1/4" long X 17 3/4" wide, the two DP side pieces are 5" wide. The 1.5" IPS alu pipe (T6061, Sch 40) pieces are 54 1/2 and 57 3/4 long - NOTE this fits DRE standard frames, NOT NRS. (For NRS, you could find Hollaender or Nurail cross or tee fittings that are 1.5 X 1.25 inches, but haven't looked).
Painted "sea foam" color that will work as primer or finish (sheds heat). Bombproof and river-wise, I slept on it a couple of trips... over $400 invested in parts, not counting welds and labor - you decide if it fits your plans. Selling because I now run monster dry box to carry motor. In SLC but could get to Moab, WW/Fruita/Loma, etc.