Keep in mind, those bikes are way behind the rear axle, so they will add far more than 600lbs to the rear axle (I'm assuming the bikes are only around 450lb as the hitch and rack will likely push 150lb). You are probably looking at the bikes adding 900lbs to the rear axle because the center of gravity for them is probably 80" behind the rear axle, so the leverage effect will transfer around 300lb from the front tires to the rear. Add in the base curb weight plus 2800 for the camper and you are probably north of 6500-6800lbs on the rear axle.
Check the specs but that is probably over the axle limits.
