I did quite a bit of research and the Surge Guard unit is very good.
I chose the Progressive Industries LC HW 50 Surge and Voltage Protection unit.
Go to Product Evaluations on this forum and you'll see some good dialouge on this unit.
I've had mine for 3 months only, but it was very easy to install and it gives me good feedback on the condition of the power at a campsite.
Good luck.