similar story, dad had an old truck with a camper, we were on our way to see my grandpa in the hospital, it was pouring like you wouldn't imagine..
I decided to go to the front, so I went through the little rear window, sat next to my mom and put my seatbelt on. No more than 2 seconds later, I hear my mom yell "NOT SO FAST, NOT SO FAST!" then everything started spinning. Hydroplaned and hit the center divider. We rolled atleast 4 times..
Ambulances were there almost instantaneously. News crew even interviewed my dad, so I'm not sure if I knocked out or what...
but me, my dad, brother and cousin were fine (even though my cousin and brother flew out the camper and landed on the otherside of the freeway). My aunt was thrown out and required a neck brace. My mom hurt her head, but otherwise we were okay..
Funny thing, is they still rushed us on the ambulance to the hospital we were going to see my grandpa in, and he ended up visiting us...