Here are my ROTAX/DUCATI VR operational data points:
3/2014 - "0" hours - My RV-12 ELSA first flown with original Ducati VR #965-335 installed per Van's plans (i.e., on engine compartment shelf with shroud and ducting).
3/2015 - 135 hrs HOBBS - Original VR (above) failed - Autopsy suggested failure due to heat and vibration - no sign of burning/smell, just open solder joints. Replaced with new Ducati VR #965-349 relocated per Van's notification to inside the cabin under the avionics shelf. I used nutplates to secure the VR and to aid in its quick replacement if needed. I did not use any heat-transferal paste under the mounting. In addition, I added a small aluminum shroud to generally route the avionics compartment fan exhaust (like warm baby's breath) towards the VR fins - not sure this is worth the effort.
11/2016 - 410 hrs HOBBS and all is well (likely this post will doom my current VR
). I typically indicate 13.9 volts and 1 amp when in cruise - frankly, I disregard all other indications (you'll go crazy trying to make sense of the voltage/amp indications during varying engine power settings) unless I see a constant voltage loss and constant negative amps during high engine power which likely means another failed VR.
I always carry a spare Ducati VR in my plane. I also try to minimize use of electrical current during low engine power periods (i.e., no lights during daytime taxiing) and maximize my current use during high engine power periods (i.e., everything "On" during takeoff/cruise/approach). Don't know if this helps the VR's longevity, but it beats sacrificing more chickens ($$$) at the Ducati altar.
My new VR is very warm when in use - I can hold onto it without scorching my fingers, but it is a tad toasty (it is useful however for warming up your passenger's left knee cap or heating up one's leftover snacks inflight). I may rig up a little air scoop on the right-side exterior of the fuselage to route some external air across the VR fins. The journey continues.....