I bought the Surge Guard 34730.
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Some teaching colleagues of mine are avid campers. They have gone west every other year for several years and to Maine on the off years. Two years ago they were in the Dakotas somewhere. The night before, they said, there was a bad storm at the campground they were in route to. When they got there to set up, everything looked ok but then they plugged up to the power and got a surprise. Their coach was "fried" electrically. They ended up staying a week and a half for repairs and ended up replacing several electrical items (don't remember everything) but it was bad. Their class C ended up with a lot of new stuff on that trip.
Before I ever got my AS they told me the story and urged me to make sure I got some kind of electrical protection along with a water pressure regulator.
The nice thing about the Surge Guard is that it tests the line, has a pause time and guards against under voltage and monitors continuously. I live in the lightning capital of the world and have seen all kinds of things -transformers hit trees hit, computers hit, cars with all tires blown that were hit. In our home I lost four entertainment center pieces before realizing it was caused by brown outs during storms or other fluctuations. I bought a panamax protector (they have undervoltage protection) and have been good ever since. We had one of those storms about two weeks ago when a cold front moved in.
The point is that it is a good thing, more money, but an insurance against other issues. We camped out in St Augustine last summer with a tropical storm. One night it was wild - lightening, wind. I had the protector on and was confident that it would fry before the trailer.