We got the 1" stems. Had the tire dealer install them when they put the new Maxxis tires on the camper. It's great piece of mind to see the temp and pressure. Had one tire go soft while in storage, the TST was right on top of it to let me know to air it up.
I would recommend the internal seniors if you can, otherwise get the flow through external so that you don't have to keep taking them off to air your tires.
2013 Jayco JayFlight 26RKS
2013 Ford F150 Ecoboost FX4
2003 Coleman Bayside / 2011 Jayco Jayfeather X20E -- RIP
2012 Tacoma Sport DCSB / 2013 Tundra SR5 - RIP