It also helps to have a dark-colored gun and a dark vehicle interior. I'm also left-handed, so when I'm shuffling the pistol, there's very little time it's visible from any angle outside the truck, as I keep my hand/gun between seat and door while transferring.
If someone -does- happen to see me fiddling with a gun, they'll either see it going into a locking safe or back into my holster. It's not in my hands very long at all. If they see me re-arming and freak, well, I'll likely never know as I'll have driven off. If they see me putting it away, and freak, they'll have some 'splainin' to do as to why they thought a locked-up gun was any threat, and a reality check as to what our rights really are.
As for "failure to conceal" within the vehicle, well, if someone can manage to pick out a gun through dirty glass and a dark interior, they've got snooping problems. Nothing criminal, but they'll certainly be uncomfortable when I ask them why they're straining to peer into strangers' vehicles, and just WHAT are they looking for?
I only conceal the pistol in the vehicle because the law says I have to. (Yes, were it legal, I'd openly carry) The law doesn't say anything about long guns, and I've gone through fast-food drive-thrus with a full gun rack, clearly visible.
So far, no-one's freaked out too badly. (For the record, the long guns were bolt-action rifles/pump shotguns. No "evil black rifles" - I really don't want to scare people -that- badly, nor do I want police attention. The local police are likely to shrug at mention of a hunting rifle, but I don't know how they'd react to an AR-15)