Over the last few weeks I did three installations for Yaesu radios. I put a FT7800 in a Toyota Tacoma, an FT8900 in a Dodge Ram truck, and an FT8900 in a Dodge Durango. I have been using the Dodge Ram radio with a mag mount 1/2 wave antenna in the center of the cab roof. It seemed to work very well and have been pleased with the results.
In conjuction with the installations, I did a "through the roof" mount in all of the above using the Larson NMO mount. It was a whopping $13 including the coax. I went through the dome light for all the installations to route the cable. The hole size required was 3/4" and I used a hole saw to cut it. You don't have direct access to the underside of the hole for the install. The mount seals against the sheet metal with an o-ring.
Anyway, I just have to say that the difference in TX and RX between the mag mount and through the roof mount is pretty amazing. For those of you who cringe about drilling through your roof, there are ways to plug the hole for when you resell the vehicle. It is also very nice to not have cables running all over the place and looks clean.
If anybody has questions on what is involved with this, let me know.