Using surge protector to check power at box?

[wmtire]

Although not as good as a true EMS which will continually monitor for bad electrical situations, you can build your own plug-n-play tester for testing outlets like you describe.

Go to this link and click the outlet testing tab on the left. It will have links on how to build your own 50 or 30 amp tester.

RV Electric

There is a plethora of great information on that site to help with all kind of RV electrics.