Hi Mr.and Mrs Mile
My name is ...In the coming summer vacation,I will go to America and join in the summer camp.So I will be arranged to live in your apartment,to be one of your family members during the camp.
I'd like to say thank you for my future room in your house,thanks for sharing one of your rooms with me.
I hope we could go along with each other pretty well during the camp.
And I'm looking forward to seeing you and your whole family!
Best wishes
And good luck
XXX