bike locks for car rack

So there are some instances when the bikes are on the car rack and they need to be left unattended. I just got a trunk bike rack, one that would fit both my car and my wife's car (it is very similar to this, maybe exactly this but a prior model: https://www.thule.com/en-us/us/products/carriers-and-racks/bike-carr...

I know nothing will be thief-proof, but I don't want to make it easy on them. I'd like to secure the bikes and, if possible, secure them to the car. In hindsight, I would have gotten a more substantial rack, maybe one that goes into a trailer hitch or something that isn't as easily stolen off the vehicle. But, I didn't, so I have to come up with a solution for my current situation (or buy a new rack). My thought is maybe a couple u-locks around the bikes themselves, then a chain to try to secure the bikes to the car, somehow. Thoughts? I've been doing research on locks in general, and have a good idea on them, just wanted to come ask here since there are a lot of people likely in a similar situation (ie - not just locking a bike to a light post). Thanks.