The problem is not voltage, but voltage drop (Also known as high resistance)
Step one.. CLEAN THE PLUG, Pull the plug and inspect the blades (forget the round one only the flat ones) make sure they are clean and shiny.
Next, watch the ??-50C (PT or HW) display while partner operates appliances, observe voltage.
If it's dropping more than a volt,,, Park may need to work on the outlet box or the distribution panel.
There is, however, one thing you might try.
Many of the park boxes use a Square D type breaker this breaker has a kind of hook at the bottom that hooks onto a metal road (not a contact) and at the top is a "Clip" that goes over a bus bar inside the box.. I have seen it happen where these have tipped forward a bit (out of the box) and made poor contact with the bus bar.. Simply pressing in on the TOP of the breaker fixes that one. (NO TOOLS REQUIRED)
When it comes to park side problems I have a rule, I will only fix it if NO TOOLS REQUIRED I do not open the box (that requires a screwdriver) but I have looked into them many times.
