If you are a Dish Network customer you must leave the power on so the antenna can switch between the 3 necessary satellites. If you are receiving your local Network programming from DirecTV on the 119 satellite then you must also leave the antenna power on so it can toggle between 101 and 119. If you use the Mini-Max only for the DirecTV SD programming on the 101 satellite then you can turn the power off after it locks in.
As you have noted, if there is enough movement of the coach after the unit is powered off it can move enough to cause a loss or reduction of the signal.
Traveling the Western US by RV