A lot of travel trailers don't have one, but if you are planning to stay in certain places that don't have access to electricity, it would be better to purchase one so that you'll have something to use for when you set up camp. You may also need additional AC power for your trailer, so it is better to be prepared in case of emergencies. Most campgrounds have 50 amp services for travel trailers, so you might have to find a generator that could also give you the same amp, mainly if you use air conditioning inside your trailers. This would provide an appropriate amount of power in case you needed it for emergencies while on the road and there is no nearby campground to stay at in your travel.