Try to contact the people offering the clinic and ask for a receipt showing the location, dates, and sponsoring organization. Keep you gun (s) in a locked device . Ammo must be in a locked container away from the gun, If I go to a shoot I have a HD black plastic storage container with a hinged top. I drilled two holes and use two master locks, one at each end. That is if I go put of state, especially NY where we have a summer camp. In NJ I keep my ammo in those shells boxes you can buy at Dicks or online. Obey the speed laws and don't give them a reason to go out of their way to stop you. Also, keep the registration papers for the gun and any firearm ID cards that you have on your possession while traveling. You can always ask the clinic sponsors if they will have ammo available or befriend a NJ shooter who could/would sell you some of his new ammo as the last resort.
With the latest change in firearm laws, which differ from state to state, it has become a hassle for legal citizens, but a " who the hell cares" for crooks, that are trying to figure them out. "
Good luck as I am still trying
Rich