Good article here from the
No Shock Zone.
I use one of the 3-light testers on a pigtail adapter cord like this:

This lets me plug the tester into the 30A outlet I will be using before I plug the trailer in. This is the first thing I do after I back the trailer into the site and before unhitching. If the outlet isn't right, I want to be able to move to another site with a minimum of trouble.
I started doing this after I was shocked once, and only ever found one other bad CG outlet in all these years of checking.
From a safety standpoint definitely invest in an outlet checker before your upcoming trip. If everything checks OK when you plug in, it's not going to suddenly change. The pricey power management units are good for surge and low voltage protection, but they are designed to protect mostly the appliances in those cases. The real personal safety issue is polarity and ground, and the little 3-lite tester has that covered.