If you live in or travel through Oregon you can check the load on each axle and even get an approximation on your individual corner weights. I did this myself last week.
There are many truck scales across the state that are open and the electronic scale are left on after hours. You simply drive onto the pad and read the total load for that axle on the display panel located on a post about 40' ahead of you.
Now if there are no trucks using the scale you may be able to simply swing around or back up and get just the right side tire loads for each axle. With those figures its easy to subtract and get the approximate load on the left side positions.
I say "approximate" as unlike the scale set-up used by RVSEF there will be a slight tilt away from the scale pad but I would think you should be within a couple percent of the actual side-to-side load distribution. I am pretty confident that most of you will have figures that are closer to the actual side-to-side weight distribution than just assuming you have a 50/50 side-to-side split on each axle.
With the individual corner loading you can then use the published Load/Inflation tables from your tire manufacturer company to learn the MINIMUM inflation you need based on the heavy side loads. Then simply add 10% to that inflation number for your "inflation margin" and you should be good to go. At least till you get on real, properly set-up individual RV corner weight scales.
Now I admit I do not know which other states provide this safety service to motorists, truck and RV owners, but for folks on the far west coast this is a great deal, at least till you are able to get the actual corner weights of your RV, or individual tire loads for trailers, confirmed by RVSEF.
If you know of another state that has scales available to the public as Oregon does, please post in the comments below as this information will help your fellow RVers
EDIT AND UPDATE 8/16/20
Locations with scales
This post relates to Motorized RVs NOT Towables. Trailers have SPECIAL considerations for setting the inflation that I cover in THIS post.
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