See 18 USC 926A.
Any jurisdiction within the USA where you cannot legally carry, the firearm must be in a locked container separate from the ammunition in the trunk or cargo area of your vehicle. If you have a truck without a bed locker, shell or lockable toolbox then you could put it behind the passenger seat as that's the best you can do with a truck without a secured bed. A loaded magazine is considered to be a loaded firearm. A charged speedloader or speedstrip is not since it is not an integral part of a revolver for it to function as designed.
The most 2A friendly path would be to go through MO, then IA. You'll be disarmed the least amount of time traveling through IA. IL could be a major problem since there are some very anti-2A jurisdictions there. In very anti-2A jurisdictions you may be cited or arrested any way and will have to duke it out in court. Even if you win, you may not get your firearms back and then have to pursue civil action against the law enforcement agency. This has been the case in NJ and NY(C). I would drive non-stop through IA after disarming in MO at your last fuel stop before traversing IA.