Cable and padlock. Most trucks have tie down brackets you can attach locks. I did that with my pickups

Tailgate pad user here. If I'm anywhere I need to lock my bike I usually run a cable lock or two from the tie down mounts through a combination of frame and wheels.

Not sure which chain / lock combo stops thieves any longer than 10 secs. Keep it inside the vehicle. Less visible is better.

Thanks guys appreciate the input

I think of any lock system as keeping casual thieves away. Any lock can be cut quick with the right tools. If the bike(s) are expensive have insurance also.

I use the On Guard Boxer Disc Lock (for motorcycles) with a Cable. that I wrap through the frame/wheels. It is small and does the trick to deter thieves. I have two of them and several cables stored under my back seat. Can also be used for other equipment when you need it like kayaks, etc. Something like this: www.motosport.com/product/?adpos=&cc=us&creative=271553284542&device=c&gclid=Cj0KCQiAkZKNBhDiARIs...[ONG000D]=ONG000D-X002-Y001

Buy a van!

Shotgun rack

I use the 5-ft version of this chain and lock. It's a beast! www.kryptonitelock.com/en/products/product-information/current-key/999485.html?type=bicycle

Big angry dog in the back of the truck should do the trick.