Explaining the purpose of the question and asking where you have been are reasonable - refusing to accept your answer and entering your RV without permission isn't reasonable. Agricultural inspections don't overrule your Constitutional Rights. I have crossed the Calif border hundreds of times over the years and never give much thought to the inspections ... but these days I would likely deny the inspector access to the interior of my RV. Probably becoming an angry old fart or likely somebody who is upset that my former home (Calif) has lost its way.