Law Enforcement needs probable cause to search a vehicle either way. If you are stopped for a traffic violation, and they can establish probable cause that a crime has been committed or is in progress, they can search your vehicle, but if this is the case, you’ll already be in cuffs in the back seat of one of their vehicles. Obviously this does not include infractions (the likely reason you were stopped).
However unless there is reason to believe someone is in danger inisde the vehicle, any cop with any sense is going to detain you there and get a warrant anyway to avoid issues. An exception to this is the “plain view doctrine”. If evidence of a crime is in plain view, no warrant is necessary to collect that evidence.
If you are in an RV and not driving (for instance stopped for the night) the same basic principles apply with the exception mentioned in the video: a warrant is required, based on probable cause (no officer discretion), unless there is reason to believe someone is in imminent danger.
During a traffic stop, an officer might ask permission to search your vehicle and you have every right to say no. This includes checking your diesel for dye (something they stopped doing here years ago). If you say no and they detain you anyway, search your vehicle, and find nothing, and probable cause was even a little shakey, you have a very good Fourth Amendment lawsuit to pursue. But they know that, so once again, unless there are exigent circumstances, they’ll get a warrant.
If during a traffic stop a canine hits on something, they will detain you, get a warrant, and search. If its near a border (north or south) and a canine reacts, they may detain you and search without a warrant based on probable cause of human trafficking, which would fall under the “someone is in imminent danger” exception.
I just drove my coach from the Salton Sea to Galveston in Jan 22, along the southern most roads possible to tour the border, and they have a lot of sophisticated scanning equipment at all the check points (there are many), in addition to dogs. So they already know how many warm bodies are in the vehcile, whether than can see them or not, and they just ask the driver “how many people are on board?” In a couple dozen check point stops, I was never asked about searching the vehicle, and the officers were always professional, respectful, and efficient.
With the exception of border areas, if you are obeying the law you will not have contact with law enforcement anyway. I’m sure there are many stories to the contrary, but after 50 years of driving, and a lot of law enforcement training, my experience has been that this is basically the case.