I'm training Melino right now... he's only 6 months old, so it'll be a while before I get him harnessed up. Maybe by spring I'll have a cart though... I HOPE!
Edited to add:I did work with Pace and Shanti when they were little and got to the stage of dragging things behind them.. but they are just too darn small! Maybe once I get a cart I'll use them as a team... but Melino is now my main focus. We just made little fleece harnesses-- nothing fancy!
As far as I know there are not plans on the internet, Alot of people have made simple day packs, which work for small hikes, but if you are wanting to do alot of long distance, I would look in to getting a real packsaddle. Easier for you and better for the goat.