Several years ago, I built some rod holders for the van and they have proven to be one of the most-used additions we have made. We fly fish only so the rack is designed specifically for fly rods but I imagine you can use them for spinning also.
Here is a picture of the "front" of the rod holder. It is nothing more than wire (coat hanger wire if memory serves) inside of some nylon webbing tape (shoe lace I believe).
In the back, I made little drop loops of nylon webbing (regular climbing runner webbing) for the rod butts to sit in and then additional loops of shock cord and cordlock to go around the reels and snug them up against the nylon.
Here's a pic with the loops empty:
Here is a pic with the rods in so you can hopefully see how the system works.
We have never had one fall out, we've never damaged one while living in the van (they are pretty far out of the way) and it will hold up to a 10' fly rod.