OCCC does not include any of the trailer weight...except the weight riding on the hitch ball.
OCCC + UVW + full propane tank = GVWR or the load that can be carried upon the RV's tires...22,000lb for all current Challengers
The trailer is part of GCWR or the total mass that can be pulled and stopped by the RV's driveline or 26,000lb for all current Challengers.
So...start at 26,000lb max GCWR...subtract the 4,500lb car = 21,500lb. available of the 22,000lb GVWR.
21,500lb available vehicle weight means the trailer is "using" 500lb of the OCCC.
So your 7 pax need to weigh-in with their stuff at 183lb each -average.
Does that work?