I've had very good luck with a RAM suction cup mount that I purchased from
Cumulus-Soaring.

http://www.soarmn.com/cumulus/ram.htm

I use the RAM-B-224 suction cup with the RPA-B-201 arm and RAP-B-238 ball.
This is attached to the appropriate cradle for your model iPAQ. In my case
I have a 3850 with a PC-CARD sleeve.

This stayed firmly attached to the canopy recently for more than 6 hours. I
can also attest to it holding firmly during a very rough off field landing.
In fact, I now remove the stylus from the iPAQ as it has a tendancy to come
out during bumpy landings.

John Scott