UKC

Car will be full but I'd like to carry a couple of bouldering mats. Whats the best way? Car is relatively new with roof bars but don't want to scratch it

- Mount tray on roofrack, mount mat on tray. Secure properly with straps. 

- Cargo tray to hard to get/expensive? Get a piece of plywood. Drill holes for U-bolts (to secure on the bars), drill slots for straps. Strap on the mat. 

- Or get a rear cargo rack, attach on towball. Attach mat on rack.

(bonus; get lockable straps if you park in less nice places)

You can pick up ratchet straps cheaply from any hardware store. 

Depending on weather, distance travelled and travel speed, just strapping them securely to the roof bars (or failing that, just through the rear windows as long as any rear passengers aren't going to want to get out in a hurry) will be fine.

Make sure the straps are very secure and that there aren't any loose ends flapping around. Soft straps are not going to scratch a car. If in any doubt or if traveling long distances, factor in stopping every so often to check the straps are still secure.