Big difference between copperhead and rattlesnake venom in how severe it effects pets and humans. Anyhow, is your son a vet? I would think legit antivenin is hard to get and expensive. Getting a dog treated at the vet will be very expensive if antivenin is administered.
Some studies suggest benedryl may help slow the reaction, as well as cleaning the wound to help with secondary infection. There is no such thing as an effective snake bite kit that includes cutting, suction or tourniquets. Its all a gimmick.
Alot of snake bites are actually dry or very little venom is used. If a dog gets a full dose of venom in neck or face, it probably wont be good if you cant get to a vet and get anti venin administered asap. Best insurance is to not get bit, second is to know where closest vet with antivenin is and get there asap.
I have a camp in a very prevalent snake area. Other than a quick pee trip in the yard, my dog is on a leash if we walk anywhere Mid may to Sept. It certainly influences what activities my dog gets to tag along for in the summer.