If you're going to be gone for four months and will be relying on your wife to care for the car, I would definitely not go the S100 route. The protection will be long gone before you get back. I don't know how long FMJ lasts, but it will definitely last longer than S100. If you have Zaino, I would highly recommend that instead because it's durability has been proven. In any case, a sealant is definitely the way to go. Do you have any of the Blackfire left? It's pretty durable. Does the car get garaged everyday? If it does, any sealant will do, but I still wouldn't do S100, especially if your wife will be taking it through the carwash.
BlkTac05: Are you married? If you are, have you been able to get your wife to wash your car for you and the way you want it washed? If you have, then you're a far better man than any of us here!:bow