was in rajasthan last year (04) in march and that was to hot.so december will be a good time to go.
my experience withe the camel ride is that it is boring. and that was allready afther one day.(i didnt had a wife), heard that from many people doing a longer trip (more than 2 days).the camp and stay at night is okay but during the day...
there is also a lot of camel maffia there.if you pick a hotel, you have to use their safari agency..or your kicked out. i was kicked out because they taught i went secretly when i was extually spending some time with friends outside in some dessertcamp.
i didnt travel with bike there but what i rember is endless stretches of sand and sand, and more and more sand around jaisalmer.
tip: outside udaipur i did a horsesafari. the best thing i did in all rajastan.
greetz and have fun