If you are needing to secure your bike upright in a minivan, the CyclingDeal Car Interior Bicycle Multi-Usable Adapter in the 13.5 to 23″ length works great. I place my bike at an angle with the front end inward towards the driver seat and velcro the front brake lever (not tight). I place a top tube protector on my bike that has a rubber-like exterior surface for added grip and security. I then secure the larger end of the the adapter to the van handle and the smaller end (small end rotates)to the bike. With the top tube protector, there is no need to clamp the adapter tight on the bike, just make sure it’s snug. The adapters come in two sizes in case you need to transport more than two bikes. The smaller adapter would be used to connect bike to bike. The road bike pictured is 56cm standing upright in a 2019 Dodge Caravan.
Read more about transporting your bike here: