Since you mention you want WiFi updates I assume you have internet available in your coach. If not you will not get traffic updates with Google but then you aren't going to get ANY traffic updates with your Garmin unless you are near a big city where there is an FM radio broadcast happening. You will NEVER know that there is a 3 car pile up ahead of you on most of the US highways. Google Maps uses VERY LITTLE data so if if you turn on your phones hot spot you won't exceed any kind of data limits.
Even if you have no internet connection while traveling you can download the entire route before you leave (while you do have an internet connection) and you will get exact turn-by-turn instructions along the entire route.