As others have said it is with the camper on the TV.
When you unhook you can check it and it should be a lower PSI and you will know the range to have it at before hooking up again. Just remember each air check will drop the PSI about two to three PSI on mine.
I know I would do it this way. Do a test to see how close to the correct air pressure you need to be what is needed when hooked up. this is very easy. then before you use the rv air up the trailair more than is needed. After you are hooked up let enough air out to make the arrow locater be at the proper spot.
I have an air hitch and I add more air then adjust after hooked to the truck. different but same idea.