Surge protectors come in two (By two by two) flavors. The last 2x2 are 30/50, and hardwired/plug in and since the first is based on your RV's power plug and the 2nd is your choice,, We will leave them here)
The important two
Spike Suppressors (I have a hard wired version) Have LED's or other indicator lamps (NEON perhaps) but no LCD display, these are designed to clip the tips off high voltage spikes, the active device is an MOV (metal oxcide varisistor) which presents a high resistance to say 200 volts but at say 400 volts it becomes a near short (Normal peak voltage in a 120 volt circuit is about 180 volts (rounded seriously) 1.414 is the actual multiplier or (Sqrt(2)).
Option 2: The units WITH an LCD that displays current, voltage and possibly other information: These units monitor voltage, some monitor Frequency and other stuff, plus they have time in timers.
When you first plug these in they do NOT deliver power to the RV but a timer starts 2-3 mintues later CLUNK and power is passed on.. If the voltage drops too low CLUNK and power is cut off, If voltage goes too high (But not enough to fire the MOV's) and stays there for more than a time lmite CLUNK they cut you off. NOTE: a true surge (Sustained high voltage) will turn your MOV's into Firecrackers (Been there when that happened, was kind of impressive) But the Surge Guard or Progressive INdustries EMS units will protect you.
Plug your 30 amp rig's Surge Guard into that 30 amp outlet at your friend's house (240 volt) and it will tell you "240 volts" (plug the spike supressor in and it may well tell you BANG BANG BANG as the MOVs go off).
Something happens and the power grid re-configurs shutting you down for like 1 second causing your air conditioner compressor to hot-start and size up. NOT WITH A SURGE GUARD of the lcd type, cause when the lights blinked off that reset the time in timer, 3 minutes later the A/C starts normally. (Been there and done that a couple times where I am currently parked)
All in all I reather like the LCD unit I have. And mine is not the best (Which is Progressive Industries)
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times