Tony, I prefered installing mine mine in the boot of the car. It is a bit of a pain as you have to switch in on before you get in the car but beside that it is OK. The sample ON/OFF can be extended so for that one there is no excuse .....
My wheelspeed sensor was mounted on the half-shaft? coming out of the diff, the RPM sensor is long enough to go trough the tunnel and I installed a 4twisted pair cable to the engine for future options (temp, etc.)
The GPS sensor sits just under the boot cover and works perfectly ... just remember to allow it locking on BEFORE you start driving, else your data is useless. This generaly means moving the car forward a few yards (like when parked against the wall at Dijon or La Chatre) or moving it out of the pitbox. I guess that parking underneath the trees at Mas du Clos would not have worked either.
If you need some more info the let me know. Did you get the CD I send you?