When I was young, I was terrified to spend the night away from home. I would stay at grandparents' houses, but if I was there too many nights I'd get homesick (one set lived 1/8 mile down the road even!). I had the same best friend all through elementary school, visited her house very often, knew her whole family, NEVER spent the night there. I'd chicken out at bed time.
I eventually outgrew this... around high school. But I still never stayed at many friend's, they'd come to my house instead.
And to this day, I can recall the fear of staying somewhere. It was real.
So I don't think making a child spend the night somewhere is the answer. In the OP's situation, she may have been left with no choice considering the other factors (weather/distance/unknown location). But for those saying he needs to at his age, I cringe. He's a kid. He may not know why he's scared, and it is truly tramatic to go through. Eventually he will outgrow this. The OP didn't say he had any problems socially, JUST w/ the overnight thing. He's just not ready. And that's okay.

to OP and son