Cat Scales tend to be Bridge scales they give you axle weight but not wheel weight.. Some folks say you should set both sides to the same pressure. I AM NOT ONE OF THEM
You really need wheel weights. First the Easy Way
RVSAFETY.COM (may need a WWW.) and follow the links on that page. reasonable price. they use portable scales and will tell you the proper pressure.
Hard way (But less expensive I think (not sure)
Find a FLAT scale. Segmented. Pull on and get weighed. Now pull around so only one side of the RV is on the scale.. That's the wheel weights for that side. Axle - wheel = Wheel weight for the other side.
Then the Tire Company Support page will have a pressure/load chart.