Fudgie

My dog is old,has a 3rd degree heart murmur and recently has been diagnosed with bowel cancer.He is not distressed at the moment and we do not want to euthanize him until the time we feel is 'right'.To complicate things we are going on a longish boat trip soon and being a nurse I would like to be able to put him down humanely myself.I am able to access certain medication such as diazepam,midazolam,potassium,insulin but unfortunately not barbiturates.Can anybody tell me whether any of these are safe and effective to use.We will not have access to veterinary services during our 6week trip and he is too well to consider putting him down before we leave.He is our much loved friend and we wish to do what is the best for him.