I believe they are viewed as warrantless searches by some George, something we are protected from by the 4th amendment.
Actually, Ca wardens and probably all wardens have been found to not need a warrant or even probable cause to search vehicles by the Supreme Court. It's why, in Calif. at least, they always have a warden along when doing a drug bust. The question before the Court involved a Calif. case but it doesn't seem to have different facts in other states unless their constitution or laws are different.
http://ivn.us/2012/03/06/supreme-court-no-warrant-needed-for-ca-game-wardens-to-stop-cars/