First the correct tire pressure may be different from wheel to wheel. So you need 4 corner weights and the tire maker's inflation chart.. That's it folks
HOw to do that method one
Www.rvsafety.com and follow the links to get it weighed. They do most all the grunt work for you but it costs a bit.. (Generally more than a truck scale)
option 2: FInd a FLAT and I mean FLAT segmented truck scale. MOST CAT scales are bridge type and those will not work (you drive up on a bridge)
Park so each axle is on a segment by itself (Be loaded for travel) get a weight ticket
Now pull around so only one side of the RV is on the scale again one wheel per segment.. Axle weight - one side weight = other side weight.
now use the tire company's charts.