Disassembled is overkill, I'm not aware of anwhere except DC that requires you to take it apart.
The general requirements of for Federal defense from local laws during interstate travel with arms is that:
-Posession of the armament is legal at the trip's origin
-Posession of the armament is legal at the trip's destination
-The armament is unloaded, cased, and trunked, and separated from ammunition
-The travel is "direct", meaning that you can stop for food, rest or fuel, but a sidetrip to a relative's house on the way to a further destination would throw your defense into question (unless that state was OK with that armament)
Examples from my everyday life:
Origin: PA
Destination: VA
Armament: Handgun
GFW State I must pass through: MD.
Stopping in MD would be a problem, as MD has a beef with handguns. If the armament was a non controversial long gun, MD would have no complaint.
Problematic Jurisdictions:
DC: DON'T STOP FOR NOTHING! (If you run out of gas, jump out and push!)
NY: Lots of anecdotal cases of out of state handgun owners being arrested after declaring their handgun luggage @ airports.