When is the best time to take down the one panel of a cot. Son 22mths old.?

New baby due Jan 2010. I'm trying to adjust his world with a few changes now and then and not all at once when the new baby is here. I've got one of those cots that you can dismantle the side panels from the cot. This is now to give him some freedom and prepare him for his single bed when the baby will be moving to the cot at about 3mths of age. Now this I've done last night, he had no problem with it, but he rolled out of his cot (on lots of pillows I placed encase) about 4 times. Will this continue, should I put the panel back or should I be strong and carry through with my plan ????