The 1200# bars are on the heavy side for that setup.
Do you have a set of the manufacturers directions? Double check everything.
IIRC Reese uses a clamp down bolt on the inside of the frame rail and a smaller pin screw on the outside of the frame to keep the saddle clamps from sliding. It has been a long time since I have messed with a Reese. I currently have Equalizer and Eaz-Lift systems.
On my F350 I don't use any WDH with the Coleman when towing my 31' Airstream I might. With the F150 we use 800# bars with the AS and 500# (lightest I could find) with the Coleman. We use the Eaz-Lift on the Coleman and the Equalizer on the Airstream.
Coleman has TW ~400# GW 3800# Airstream TW ~600# GW 7200# but usually is only loaded to ~6200#.