I took some solid bar stock and heated it red hot and hand bent it 90 degrees…then I counterbored a hole thru for the stock seat bolt leaving a .125 thick floor..
Tapped a hole in the top for a 1/4-20 screw to attach the top plate with… The rear mounts utilize the stock backrest mounts with a couple sleeves to achieve the proper height to sit just above the passenger seat area..Top plate is 1/4 alum with rounded corners…Painted everything gloss black..
The entire build took me one day at a buddys machine shop..I had the aluminum suitcase laying around and ordered the chrome rack ( fits a harley tour pack) for $57.00…
Guess it helps that I am a retired tool and die maker…

a1scoot