how about trying to build up to it before the vacation? let your husbands parents take him over night one week, then for two nights another and three nights another. that way he will see that you always come back and he will get used to being there.
also, i use rescue remedy to calm dexter down when needed. you can buy it at any natural health store. i spray it on some treats and he gobbles it up. i use it on myself too for public speaking.
