To use 50 amp RV on 30 amp site you use a dogbone adapter
To use PT-50C you .... Plug RV into PT-50C same as always
Plug PT-50C into DOGBONE
Not only will it work.. but the PT-50c provides several services, ONE of those is spike supression (The lower cost units without the LCD also do this, but most of those do not have the other features of the 50Cs)
Not only does this function still work,, it works BETTER when on 30 amps. But, You will very likely never notice that outside of a test lab.
I might add, you can use a 30C on a 50 amp outlet with a dogbone if you have a 30 amp rig too.
Home is where I park it!