Well, if the beach chair wasn't a great big hint, daring you to ask, I don't know what is. But perhaps his plan is to spend the day at that lake tomorrow, but not stay at her place overnight. I'm sure that he would consider that a huge sacrifice in deference to your provincial attitudes. blech.
I know you don't want to call your MIL all the time, but tonight and tomorrow night you might just want to try her number first when it is time to say goodnight to the kids. Unless you really don't want to know, which would be understandable as well.
