In the past, I always drained it at the end of every trip. Even if that was just a week-end get away, or a week trip. On the return home, I'd drain it.
This year, I have not drained it was filled in March. Why? Because we are using the camper, pretty much 24x7x365, camping and at home in the drive way. I haven't seen the inside of my house in almost 2 weeks, except to do laundry and swap out food in the refrigerator.
The guy at the RV shop is correct, in the fact, that draining often rids the tank of the lime and build-up sediment. If not using the camper for any length of time it's a good practice.
However, if using the camper, and running water through it constantly, then it just doesn't make a lot of sense to do so.
However, if I knew the camper would be sitting for more than a couple days, not being used (even at home), then yes, I'd drain the water heater.
I think the decision to drain or not to drain depends upon how often you use the water in your camper, making it an inconvenient task.
Definitely, if the trailer is setting dormant for more than a couple weeks, it's probably best to drain, for peace of mind if nothing else. No water in the system means nothing to leak in the event of something going wrong (or foul play with your camper.)
