You've opened up a can of worms This is a much discussed topic by drivers and those involved in the trucking industry, particularly those involved in the DOT compliance side of the business.
Ok, first, my disclaimer: I am not a lawyer, and am not qualified to give legal advice. You absolutley should check with an attorney on this subject. The following is only my interpretation of what I've been told over the past 8 years, and is striclty my personal opinion formed from unofficial conversations on the subject.
Now, for a little background, from 2000 to 2002, I was an OTR truck driver, and was a fleet manager for a 43 truck fleet for 6 years from 2002 to 2008 in Indiana. I was asked this question so many time I lost count...so being the fleet manager of a trucking company, with an OUT OF STATE (Kentucky) weigh station just 6 miles south of our terminal, I did what any self respecting, gun loving, truck driving, fleet manager would do. I went down there and asked them. We had a pretty good relationship with them, and spoke with them on numerous occasion to learn their intepretation of laws, so this wasn't anything out of the ordinary.
What they told me is that the peacable journey law is a federal law that applies to everyone, regardless of vehicle type. It is NOT specific to CMV's. They advised that if I were to search the FMCSA regulations (these are the laws that govern CDL holders and commercial vehicles) you will find that NOWHERE is there a reference to firearms. In fact, the only references to concealed weapons relate to drug testing provisions and collection sites.
The scalemaster summed it up to me like this: There is no FMCSA law that prevents a CDL driver of a CMV from legally carrying a firearm in accordance with the regulations of his home state where his permit is issued, providing that he is in his home state OR another state that honors his home state permit. He said that the only restrictions or problems would be from state to state and some metropolitan areas depending on how those states/municipalities interpreted and/or honored his home state permit. He also added, that he and other officers he knew had no problems with a driver legally carrying a firearm under the above conditions. However, he did add that the general demeanor and conduct of the driver would determine how the situation was handled; i.e. if the driver was 100% legal on hours, paperwork, equipment, etc. then they wouldn't even pursue investigating his CCW as long as he had a valid resident or non resident permit. However, if he was behind on logs, had unsafe equipment, a bad overall attitude, etc. then he 'implied' that they would follow every paper trail they could, even pertaining to his CCW status in order to find and issue every violation possible.
Now, lastly, I CAN tell you that very few companies will allow their drivers, either O/O's or company, to carry firearms either in the truck or on the property. This sometimes is simply a company policy, but in many cases it's a requirement of their insurance carrier. In the trucking industry, the insurance carriers have more control over the drivers and equipment than the actual trucking company does! Add that to the fact that truck drivers are often over worked, under rested, and under paid, and you have a very emotional situation where they don't want firearms to be a part of the equation.
FMCSA regs do not prohibit gun possession in commercial vehicles. Everyone however, is subject to the laws of each state and most carriers prohibit firearm possession as company policy. If your buddy goes into KY and they recognize our LTCH, he should be good.