I actually installed 2 of these in my trailer. My 64 had a white dome in the rear, and a flat aluminum in the kitchen, so I chose models close to those. I have a couple comments. 1, they are fantastic. Quiet, and move a ton of air.
If you get the flat roof that VTS sells, the motor is a low profile - which means you can't see the motor when the vent is open. I like that look a lot. If you look at my trailer, if both vents are open, you can see the motor in the one that has the dome, but you can't see it in the one that is flat. I would have preferred they were both low profile motors just for the looks, but the traditional motor is just a little bit quieter.
Haven't needed the customer service, but I'm glad about the reputation. I've been running the fans pretty regular during the day to keep the heat in the trailer down. I also put bubble foil on the windows on the south side. Seems to help a lot.