You don't need to soak a crown as you maybe would a whole turkey, as being only the crown it tends to cook a lot more evenly (no cooked breast and raw thighs situations!).
If you're going to soak it i'd suggest a light brine solution of water, sugar, and salt, with whatever other flavours you prefer - maybe some bay, peppercorns, orange zest, corainder seed, onion, sage, etc...
Our friends did roughly what donquixote recommends to the whole turkey which they then bbqed. It was delicious, moist and very flavoursome. OH had his doubts when he knew what was going to be done, but even he was won over.