The bears don't climb on the roof, they simply roll the van over or tear the doors off, depending on whether or not you're cooking bacon inside. Bacon is dope for a bear.
Mountain lions, however, are another thing. Their preferred mode of attack is to jump on prey from behind and sink their fangs into its neck and sever the spinal cord. So, when getting out of the van, always first "face" the roof and see if a cat is up there. They say that in places like India, people will wear a hat with a painted face pointed to the "back", which will tend to dissuade Tigers from sneaking up behind. Then, the 2nd thing to do on exiting the van is look underneath to see if any rattlesnakes have roosted overnight. I have a morning checklist, myself.
It also occurred to me that the birds and squirrels on your roof can be dealt with by throwing some food onto the ground away from the van. Then they will come down and eat it.
NOTE: of course, this is opposite to what the rangers all say about feeding wildlife, but might save your solar panels.
