Steer clear of the lowest price surge protectors as they won't offer the addtional features of the higher priced units, most particularly protection from excessively low campground voltage which is not uncommon at all. The two leading brands are TRC (Technology Research) and Progressive Industries ... I've owned both brands but many if not most on the forums would give the nod to the Progressive units because they carry a lifetime warranty. Their EMS units are available as both portable or hard wire ... I chose the hard wire but many prefer the portable because it's so easy to use - just plug it into the campsite power post and plug the trailer's main service cable into it. Since your trailer is wired with 30 amp main service the Progressive portable unit EMS-PT30C would be an excellent choice. Some do nevertheless choose the 50 amp version which will also work just fine with 30 amp service as it can later be used if they upgrade to another rig that's wired with 50 amp service. Personally I'd buy the 30 amp model for your current trailer as used Progressive EMS units priced correctly are easy to sell, allowing you to then buy a new 50 amp version when you upgrade to a different rig that requires it.
