I have had a Doran 8 tire monitoring system for about 2 years - 4 TT tires, and front and rear truck tires. Just returned from 2500 mile trip and it performed flawlessly. Installation was fairly straight forward.
My initial system test last year had some trouble reading one of the rear travel trailer tires. Doran actually made an unsolicited call to see how the system was working, I explained that occasionally would lose sensing on one tire, they had an upgrade and sent me a whole new system at no charge. They appear to be very responsive to customers.
This last trip as I said system performed perfectly. It gave me a warning on rear truck tire, pressure had dropped the required about 10 % (forgot the actual per cent) I looked at the tire, looked ok, but futher inspection - sure enough showed a nail present and problem corrected before anything serious happened.
I leave the sensors on the tires even when not hooked to TT and monitor truck pressures. Also can check Tire pressures on trailer in back yard from truck in driveway - beats crawling around with tester. It is very interesting to see how much the pressures vary when on the road. I start with 55# truck front, and 65# on rear and travel trailer and they will run 10# higher ie 65# front and 75 to 79# others when running at 65-70 MPH.
One interesting effect that should watch for - was on vacation for 2 weeks temperatures dropped to around zero degrees which was enough to drop the tire pressure and set off the alarm, which continued to go on and off for the 2 wks - battery was way down when I returned so now unplug when go away during cold weather.
I am very satisfied - don't know yet when will have to replace valve stem sensors - it has been 2 years of continuous use. I have a dash mat and it attaches with velcro.
http://www.geocities.com/dgullick1/Dorian1.jpg
It is very reassuring to be able to check on those rear trailer tires when traveling down the interstate.