Not as a TSD but as a TKD, I entered several "open full-contact karate tournements". I have to say well in my defense that I always practised "old school" TKD what looks more like TSD meets Muay Thai and not the olympic competition form it has become nowadays.
The best way to prepare yourself for such a competition is to find a kyokushin karate club and ask if you could train the sparring with them, first easy later full-contact.
Some clubs (mostly the ones that remember that Mas Oyami was Korean by birth) will not see any difficulty by that if you would pay insurence and a smaller clubfee.
That was my training routine.