Can't help with your 31.5RLDS, but my 28.5RLS needed to have the receiver and additional frame reinforcement fabricated for the trailer by my hitch installer.
Am taking the 5ver and boat out for a week's RVing/fishing tomorrow. Can't wait!
'06 2500 Silverado 4X4, Duramax LBZ Diesel, Firestone air bags
'08 Tracker Pro Guide V-16 Boat
'12 Pinnacle 31RLTS