So - I’ve been doing this basically for all the time before my local furry convention - customised t-shirts. Many of them were custom bases too so I’m pretty happy with how I made it work ^^;
Note though: they won’t end up looking -exactly- as these mock ups, but as close as the printer can allow.
So yeah, I already got my t-shirt (guess which one is mine lol) and I’m pretty happy with it. Looking forward now seeing the rest printed ^^