Thanks Chris. The RVND5510 looks nice, and seems to do what I want, except for traffic updates. I also wonder if it is difficult to use as it is a windshield mount. Natalie leaning across me to get it for an update may be a distraction!
The Kenwood is what they recommended at Liberty, but it does not seem to be bus specific. There is already a radio in the bus, so a car GPS doesn't seem that helpful, especially for the massive install prices.