The Pressure Pro is a popular model of tire pressure sensor that is easily installed (less than 30 minutes and no tools) on any RV, including truck & trailer. It can monitor both the tow vehicle and trailer tires - see http://www.advantagepressurepro.com/
Installation is easy - just plug the monitor panel into a 12V (cigarette lighter) outlet and screw the sensors onto the tire valve stems. You can attach the monitor panel to your dashboard with velcro or double sided tape or just let it sit/lay free if you like. It doesn't even need to be visible at all times - an alarm will sound if your attention is needed.
One of our members, Bernie Dobrin liked it so much he now sells them to other RVers. I got mine a year ago from www.rvupgrades.com and have been happy with it - it "works as advertised".
How do they work? They replace the valve caps and the replacement caps have small, battery powered radio transmitters in them... They report to a receiver/compuer which is very small and attaches to your dash or visor using clips, velcro or screws, very flexable mounting
They work very well and report tire pressure either about once every five mintues or when there is a sudden change or a 10% drop in pressure. Normally the display is slient and dark, unless there is a tire with low pressure
Instalation is as easy as checking your tire pressure
Where do you get them... BernieD, a forum member, sells them