At one time, I did the rain guage thing. However, since it was the tilt/bucket type, it made it very hard to get "real" readings from it. Forget using it while your moving. The bucket bounces around so much that you get 5 inch readings on a sunny day!
There are newer sensors out there now that utilize an impact sensing routine, though I don't know how accurate they are.
Another thing to think about while you have all the nice frilly bells and whistles on top, they are all subject to wind resistance! Make darn sure your mounting is secure. The other thing your subject to are the suicidal meadowlarks (and other various flying creatures). Hitting one of those at 70 mph is going to do something. Usually it's a mass of guts and feathers to clean out, but occasionally it results in structural damage to the equipment not designed to be hit with stuff like this.
I've pretty much done away with the Sensors though. I've found that about the only one I really miss is the Anemometer. So I'm looking for a reasonable solution there. Other than that. The temp sensor on my vehicle works just fine and if I really need more detailed information, there's nothing like pulling off the side and pulling out the ancient sling psychrometer. That gets more stares that even a fully decked out storm mobile!