Hi Paul,
I have sent you a message on the rhubarb wine, & then I read this post, so for your info (& anybody else`s) For your port style wine use the Gervin GV4 high alcohol yeast. Now sold by Muntons through the home brew shop. When Gerry Fowles first introduced this we used to hold regular wine tasting sessions & he was still working at the University, I made a Dessert wine with this yeast & he analysed the end result to have 19% alc. This is very good purely through fermentation, so it is the one to use for the style of wine you are trying to make.
Cheers, Adrian.