Dave says:
If he thinks he has just cause, he won't ask, he'll just search.
The question that is posed in this thread is whether to *consent* to
a search when *asked*. (If they have probable cause, they don't ask.)
So if they ask, say NO!!! They *know* that if you say no, that is no
basis for probable cause, and they cannot then search based on your
answer.

JB says:
Dave, have you ever been asked by the police if they can search your
vehicle?  Again, I'll add that I've been searched 4 times in 7 years and the
one time I refused turned into pure roadside chaos with dogs and cops and
the interior of my van strewn all over the roadside, they even removed the
drivetrain to get the fuel tank...('69 bay).
I hate to say it but if one refuses a police search, they are likely to be
searched anyway by cops who are now highly suspicious...i.e. probable cause.
I say you are right in your assessment of the legalities but there is also
the "real" world where drug confiscation brings with it monetary value by
way of vehicle/house/plane impounds that end up in auction with proceeds
going to the agency which performed the confiscation.  Happens all the time
in my state of Missouri along I-44.  The MSHP now owns more semis and SUV's
than guns and generates more revenue from this than from speeding tickets.

JB -never caught with anything but searched more than I'd like.