You described, more or less, how I do things.
On a 50 amp site: I use the washer outlet (Since I do not have a washer) and a heavy duty extension cord.. PLUS I have 3 heavy duty outlets here in the motor home.. These are 15/20 amp outlets, each one has a breaker all to itself 12ga wire to the breaker Some are 15 amp some 20 on the breaker.. Save for one special outlet.. that one is shared with the Rear Air Conditioner (Argument I will never need both at one time).
The Rear A/C power runs to an outside compartment, there we have plug and socket, So on a 30 amp site it "Breaks out" and eats independent of the rest of the RV.
There is also an extension cord. originally I just put the slide out half way, fed the cord out and finished the slide, I finally routed it through existing openings down into one bay. This too can eat off the 20 amp outlet on the park side. What configuration I use depends on the site and the need.