Ok my take on this. I feel if it's a "free" trip, why do you need to give them anything, even if it will be returned to you at a later date, and especially a credit card number? What was the reason they gave you for the $50 deposit so to speak? You won, you shouldn't hand over anything but your regular entry information (name, address, phone, etc) to receive your prize. The $50 should be paid by them, not you, you're the winner. I've always been cautious when people want my credit card or checking account number for things camouflaged as free. Maybe you can call the Better Business Bureau in your area and ask them what avenues you should seek in finding out what you need to make your final decision....but girl I don't know about that credit card thing though. It's too much going on in this world scam wise.
I've won a free trip to the Bahamas in the past, was it legit, could have been, but when they wanted me to send a check or money order for fees, as Jill Scott said, "Please, I decline."