Hi Liz,
We breed and train gundogs for both work and competition and sometimes we have this issue with puppies that we are running on for training, so here we go?
Firstly, how old is the dog? Are you confident that s/he has never had a bad experiance?
Secondly, to deal with the general stress ask for vet for a DAP collar. In the UK one can also get a DAP spray, but I have not found it over here. It is similar to feliway spray.
Thirdly, start making loud noises when the dog is fed. I Start by dropping a metal food bowl on the floor some way away from the animal. It is trial and error till you find a distance at which the dog does not react adversly. As the dog starts to ignore the noise, decrease the distance. Also start to change the sound, burst a blown up paper bag, shout 'BANG', even burst a balloon. Slowly make noises outside of feeding times, but ALWAYS give a reward when the noise is made. Our aim is for a dog to either sit at the sound of a gun going off at 10 metres from the animal, or sit by one's side while one fires off a 12 bore shotgun. You do not need this type of standard.
Lastly, does your dog retrieve? If so aim for the dog to associate the reward of a retrieve with the loud sound.
Hope that this helps