I like TireTrakers which saved a friend from a serious problem. See details in this post:
http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27901642.cfmYes, just unscrew the silver "fill-through" caps that TireMan provides and screw the TPMS units on.
Here is a picture showing the TireMan extenders, the two TireTraker sender units, and the TireTraker display:
**NOTE / UPDATE** The rubber grommet is supposed to be installed on the wheel itself, not the wheel simulator as shown in this photo.
The labels mean left inside and left outside, to avoid getting them mixed up.