As far as I know, no special gauge is necessary. Make sure to check the tires COLD to get an accurate reading. suspect you have 'D' rated tires due to the low(er) pressure. If 50PSI is your max, keep it at that. Relieve pressure if necessary. There has been lots of discussion on nitro filled tires...here on FRF along with various sports car message boards. I think nitro filled tires trickled down from the aviation community where altitude would freeze water molecules in the tires and that's not a good thing for high speed balance. The general consensus is that nitrogen for land based vehicles is good for it's 'dry' component(lack of H2O)in the fill, but totally a sham. Good ol' air from your gas station will be sufficient. Good luck with the new unit!
2010 Cedar Creek 5th Wheel 34SATS "The Beast"
2006 Ford F350 Lariat 6.0L Diesel
2003 Harley Heritage Softail "Hogzilla"
1988 Harley Softail Custom "The Fireman"
1986 Marriage to "Wifey" (patience of a saint)