Link for the microwave that came with our new Minnie:
http://www.amazon.com/Advent-MW912BWDK-Microwave-capacity-adjustable/dp/B0061H4I4A/ref=sr_1_2?ie=UTF8&qid=1378641996&sr=8-2&keywords=rv+microwave
Our trailer is new, so I can't really tell you anything about this Advent microwave. We're headed out for a shakedown cruise on Tuesday, and after that, I can tell you my impressions of the Advent, and whether it's worth spending more money to buy this for a RV replacement unit.
Panasonic alternative (not specifically for rv)
http://www.amazon.com/Panasonic-NN-SD372S-Microwave-Technology-Stainless/dp/B00785MVRA/ref=sr_1_3?ie=UTF8&qid=1378641996&sr=8-3&keywords=rv+microwave
If you install a non RV unit, you may have to do a little trim work to get it to fit properly. So, the decision to go this route may depend on your DIY skills.