I have been to several campgrounds with 90 PSI. One, Corp of Engineers park with 125 PSI.
Checking the pressure before connecting is not a reliable indication. Dynamics in the park can cause wide pressure variations.
After setting an adjustable regulator where you want it it will be fine wherever you go. Its whole purpose is to regulate pressure irrespective of the supply pressure. The only time you will not get the pressure you set the regulator to is when the supply pressure itself drops below the regulator setting.
To not use a regulator is asking for trouble. The guy at Jayco is fairly sure he will not have to deal with the consequences of your plumbing failure.
Chuck - Sparta, TN
2012 Jay Flight 22FB, 2 x Honda EU2000i
2013 GMC Yukon XL Denali AWD
EDUCATION is what you get when you read the fine print.....
EXPERIENCE is what you get when you don't.