It is best if you can get to the power peg with your 30 amp cord. Then use an adapter right there at the peg. If your PC provided cable is too short, it's better to have a 30 amp extension. This way you are better equipped for other situations when 30 amp service is available but too far away.
I had bought two 25 foot 30 amp extension cords from Menards on clearance for $15 each. It's not a good idea to get too long like that, but it's much better than a 15 amp extension cord of the same length. In all our travels, I used one extension cord one time, in Black Canyon Of The Gunnison NP. They actually had a power peg in the camp ground, very unusual for a national park. But it was not close enough to use the PC cord alone. I also recall there were a few power pegs in the Badlands NP campground. but again, too far for one 30 amp cord to reach.
Come to thinking about a quick remedy adapter, Walmart sells a real small adapter with no cable in between, just like this. It is very affordable and readily available.
