This is my first post as we are in the process of ordering our first TT - a Timber Ridge 270DBHS. We have only tent camped in the past so knowing how long the pad was didn't really matter at the poin...
From my experience RV'ing for the past fifteen years, they list them by length of the trailer, and normally there is space next to or in front of the trailer for your tow vehicle. There is always the exception, so if you are making reservations at a particular camp ground just ask them.
For what it is worth: about 75 percent of the camp grounds don't have pads