The next picture should give you a better clue how I mounted the RAM mount:
It is possible to fix the Otterbox in various positions, even in unusual ones :) :
The whole thing weights about 700 gramms (including the N810):
Here’s a closeup:
The box protects the N810 perfectly. OTOH, all controls are inaccessible when the N810 is in the box. It would be interesting to place some buttons on the Otterbox to control the pan and zoom of Maemo Mapper (an excellent application, BTW).