I would recommend a TPMS. The one I use is sold by Truck System Technologies
. The one I bought the battery is only good for a year (replaceable) but the tire can be aired up without removing the sensor. You'll have to pick up some Wheelmaster 135 degree tire extensions to get them to work on the rear outside tires.
There's several other after market TPMS that will also fill the bill. This is another popular brand RV Tire Pressure Monitoring Systems by Doran
. I see Amazon and camping world sells them, so you have plenty of choices.