In response to vehicle carry, I asked the sheriff in my county about that, and he said that a firearm may be accessible to the driver IF the driver or a passenger has their permit to carry AND that firearm belongs to the permit holder. Otherwise the rules are as usual... inaccessible to driver, unloaded, and in a case of some sort.
I agree with mrjam2jab that your sheriff is blowing smoke. Here just south of you in Missouri we had the same sort of B.S. from anti-gun, anti-armed citizen LEOs when we first passed CCW. Your sheriff is simply trying to negate the law as far as he can by giving you false info about what you can now do.
You don't say what county you're in. The IFC (Iowa Firearms Coalition -- Link Removed) is doing a great job of correcting and/or publicizing these sheriffs so that they can be targeted for defeat in the next election. But they can't do that unless people like you report who the sheriffs are and/or which county they are from. Knowing that one sheriff out of 99 is giving false information is not helpful. It's just complaining for the sake of complaining. Knowing which sheriff is giving out that info is helpful. Then action(s) can be targeted to correct the situation.