Hi,
If you find yourself between Chamonix and Switzerland around lunchtime or tea time, then there is an idyllic stop just here (not a car park, rather an off road stopping area):
46.075687, 7.020623
(to see where it is you can put those coordinates straight into
http://maps.google.com)
Alternatively, up the hill a few bends there is a village with touristy shops. but the view is better at the road side stop in my opinion.
Its in Switzerland, so strictly speaking you cannot wild camp, but I imagine this road side stop frequently finds itself having the odd MH in it.
cheers,
twinkly