That's basically correct. Ships used to mix the wine with brandy to increase the abv because they could only carry so much.
My dad and I have a blackberry "port" on now (the recipe uses inverted commas too, its not really port) - blackberry juice, raisins, sugar and gervin high alcohol yeast. I'd imagine with some wood ageing it will taste amazing! Just an idea though. Any deep red with some complex flavour at 20% would be great.