If you want extreme budget a cinch strap and a towel is how alot of surfers carry their boards out here. I've also seen people wrap foam with cloth or tape or both and make a couple of soft "boards" out of em then just strap though the doors. Otherwise I think amazon, and others can find you racks for the roof for around $300. Then there is always DIY stuff for the bed. Anything you can dream of can work back there.
Sponsored