Sevenoaks School exam - is 11+ tutoring enough?

[WitchOfTheWaste]

DS will be sitting the 11+ in a year's time but we are also looking at Sevenoaks as I've heard fab things and I love the idea of co-ed and international focus. He's just started some 11+ tutoring and is loving it so far, and seems to be doing well. Our current plan is to enter him for S'oaks exam as well, and just do some past papers for a couple of months once he's finished 11+. He's currently at state primary, so no specific help/guidance from the school. Is that enough to give him a reasonable preparation? Or do we need to consider specific tutoring? Want to give him a good chance of a place but don't want to go crazy-parent about it all.