I've got have some great news to share with you today!
While MultiMerch is compatible with third party OpenCart themes, some of them may require extra integration by your developers.
Since we want to make MultiMerch compatible with as many great themes as possible, we've partnered with the guys behind ShopMe and CosyOne themes for OpenCart. Their themes are great themes in terms of code quality and customer support and we absolutely recommend them!
Check our this detailed ShopMe installation & integration guide we've published just a few days ago – this covers the whole setup process from start to finish: MultiMerch with ShopMe Theme & OpenCart
Here's a preview of what ShopMe looks like with MultiMerch:
P.S. We'll be publishing an update to MultiMerch 8.2 shortly, stay tuned!