If it was locked in a case under the seat and not readily accessible, then technically I would say you were NOT carrying concealed.
The fact that it was
loaded takes it out of clear transportation situations (not accessible to the driver, unloaded for transportation, etc), and into a grey area where it isn't well-defined (not accessible, but not correct according to interstate transportation rules either)....which is another way of saying "we don't know because there isn't a clear answer, so the only way to find out would be in court."
...and you probably don't want to do that.
Note: This isn't me disagreeing with Chris, I personally think you can't be "carrying" when it is locked away from you. However, that doesn't mean that law enforcement will agree, and the law itself on this is....non-specific.
My personal opinion is that if you have a loaded gun in the car, inform. If it is unloaded but on your person, inform. If it is unloaded in a case, don't worry about it.