Well you said the Surge Guard kicks you off from time to time.. This indicates a problem park-side.. but Reading on
You tested all outlets and all tested good save the M-Wave low.. Several causes of a low voltage reading, but most of them are "Fatal" (meaning the M-Wave wont't wave) Note that everything on this list I have seen first hand and I AM NOT a professional repair technician.
I have a Freezer here beside me sucks 12 volts.. all of 3 amps at 12 volts.. It failed, Measuring voltage at the distribution panel in front of me showed 11 volts (House voltage 13.6) no load.. Loaded it was closer to zero.
Found a bad wire. Believe it or not the wire itself was bad,, Mid run.. Fixed
And later a bad connectrion (Same wire, battery end)
My Air Conditioners back when this house was basically NEW. one or the other (or both)would or would not work.. Well, First thign I checkd turned out to be close enough... I opened the Power Distribution panel (Breaker box) and in "poking around' (Safely with caution) Noticed wires moving about that shoudl have been clamped tight.. They are now and the A/Cs work fine.
Now: Suspect #1 in your case.. Also a park problem.
Note the L=1 and L-2 voltage readigns on your Surge Guard.
I am guessing one is low (Matching the M-wave outlet in fact)
Alternative go to your breaker box.. Assign a number (1 or 2) to each breaker in such a way that you can tell which leg that breaker is on I am guessing most of the outlets in the RV will be on one leg but the MICROWAVE will be on the other.
One leg has low voltage, This is what is kicking off yoru Surge guard too so it's a PARK side issue.