I've been to a lot of campgrounds up and down the east coast, but mostly in and around VA - both state parks and private campgrounds. I have yet to find one where my stock 25' cable hasn't worked. If it looks close, I'll check that first thing before doing any other setup. I think I've had to adjust once by a few feet.
Not to say they aren't out there, but they're more the exception than the norm in our area. I do have another 25' that I bring with me, but it's still unused.
In your case, it really depends on where they're measuring from and where your power cord is located on your trailer. If they're measuring straight back from the road, 79 feet is likely pretty good. I.e., my truck is something like 24 feet, and trailer is 32 feet and I rarely have the truck right at the road (maybe 10' back), so that would put my power cord within about 15 feet from the pole. If they're measuring from the pad straight out to the side, you're definitely going to need something. Usually a call, drive-by, or a visit to something like
http://campsitephotos.com are usually the only ways to resolve it positively.
During cooler/colder weather, you really don't *need* 30amps unless you have a heat pump or need to use an electric heater. If you have a regular LP furnace and don't use high draw items like the A/C (or heat pump), the microwave, electric heaters or hair driers, you can get by quite well with 15 amps. I always carry a 30A->15A adapter and about 100' of 12ga 15A extension cords just for that reason.