We do state parks and have put my 34' trailer in several "30 foot" sites. I have not had an issue in 8 years, but just be aware that many sites are rated not just on overall length, but on pad configuration, ie, the trailer area and the lead-in driveway are two different angles or elevations. You can run out of tongue jack before you get a longer trailer level.
It's very disappointing to get all unhitched and set up to find out your tongue won't go high, or low engough. You have to be able to read it before you unhitch. Going higher isn't too much trouble if you have some blocking, but when you can't go low enough, that means the whole trailer must be raised (pads under all axles in additions to what's needed for side to side level). Every time I have some slope front to back I always consider adding height before I unhitch just to be safe.
