I used to use the GPS III in my Jodel on my kneepad. It took about 5 minutes to knock up a bracket. It worked perfectly.
I've now gone to a 295, and can offer a cautionary tail.
This has to sit on the coaming as theres no room elsewhere. I checked it for compass deviation and got 2-3 degrees with it right next to the compass. No problem I thought.
Then on one trip I swapped batteries to return home and started noting odd compass readings. It turns out that the spare batteries (Varta 1500 mAh NiMH) are much more magnetic and gave me about 30 degrees of deviation. Be warned, or take a compass with you when buying batteries.