Tyre Pressures on Jayco vans

For everyday use for the vast majority of tyres in use, air seems to be quite good.
There is no normal discernable advantage in having nitrogen in the tyres,
Most people regard Jayco as using nitrogen as an attractive sales feature. Gimmick.
If it was a racing caravan then maybe.

Nitrogen has larger molecule size and doesn't leak through rubber as quick as oxygen and CO2.

If you leave an inflated tyre for long time some gasses leak through the rubber and what is mostly left is nitrogen. Reinflated with air the tyre then has more concentration of nitrogen than when originally filled with air.

If you regularly check your tyre pressures and reinflate them with that common stuff "air" you will never know any difference. There is a fair percentage of N in air so that last little bit that Jayco by using all N is good for their bottom line and not yours.

I have the nito in my Jayco as well. One benefit I found was when I went north last year, there was no expansion from the heat. I never bothered reducing my pressures, but most of the trip was on the black top.

Why would Jayco fill their hoops with 100% nitrogen..?

I'd say just fill them via your compressor and be confident that they have 79% nitrogen in them, courtesy of our atmosphere.