Just did this on a drive from VA to TX and back this week. My VA permit is good in VA, TN, not in GA (we cut the northwest corner of that state on I59/24), AL, or MS, but good in LA and TX.
I did what everyone here suggested: Our last stop before the GA border, I unloaded the pistol, put the mags in a separate bag, put them all in the trunk and didn't take them out until we hit Louisiana. Did the same thing in reverse on the way back.
Go to
packing.org, look up the state his permit is from, that'll give you a map of which states it's good in. Go to the individual states you're going to be crossing and print out the relevant sections on how/when/where to carry, and the "peaceable journey" or "car carry summary" sections for those states the CHL is NOT good for and follow that.