Hi @scooke ,
To your question, I followed the instructions on the Garage website, and I added a near-copy of that documentation to the README in the package I've developed. This is all documented in the git repository for the package that I linked to. I have Garage running on my Cloudron instance, and was able to create buckets, add content, and even serve static web content from within those buckets. I'm sorry your prior experience with this did not work for you.
I am now trying to do that in a way that it would be considered for inclusion as a standard package, if the Cloudron team thinks it is worthwhile. If they don't, perhaps I'll do it for myself.