When in this type of tit for tat battle, it's pretty much of a no win situation for the LBS, from what I have seen. I think it might be to your advantage to tell your W about the trip. If you act as if you are being secretive and wait to the last minute, she'll sure enough try to scr@w you. What do you have to lose, by being honest and discussing it in plenty of time? Having grandparents as backup sitters would be my call, too.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!
