I have heard pros and cons regarding making double batches of port in the 6 gallon carboys as opposed to the single batches in 3 gallon carboys. Is there any reason why double batches are not a good idea, as long as one uses ALL of the ingredients provided for the kit? Many on the discussion forum were complaining that they were not reaching the required SG, but then most of them had changed the recipe and had left out some of the ingredients, ie yeast, nutrients, etc.