Annnnndddd the other shoe drops. 
We have been running an Internet based project for years and I can confirm that source control over the InterWebs is a Myth once the need for art content becomes involved and in general art content does not like GIT at all period. With GIT you have to do this that and the other thing just to get it to work and as you found out the more you add the more miserable things become just to share some project files.
We started out using git and all that fun in-app source control but we discovered real quick some major issues that there is no “single” solution that would make life easier and in no particular order over time this is whats going to happen based on a single solution.
- In app source control loves to lock out project files that does not need to be locked out as part of a team effort. For example coders can do their coding thing while content creators can iterate the art with out stepping on each other toes but in app source control will lock out any changes once the project is checked out and not available until checked back in. If the project is locked out over the Internet it’s not like you can walk down the hall and check the project back in so you land up most times breaking locks which defeats the purpose of having source control in the first place.
So in concept “source control” only works on the local level and best served if you have a large team working on the same project at at the same time
To solve this issue is we simplified our source control procedures using a simple solution.
“Hay Bob don’t mess with such and such project as I’m working on it at the moment.”
Believe it or not working on a small team it just works.
- A single source channel does not work period over the Internet. When you combine code with content what is needed by the two groups is totally different as to usability of that group. There are a lot of problems but the big one is the shear amount of data traffic becomes massive the more art content that is added to the mix, aka lfs, and something like working on a single environment can grow to over 100 gigs as the working assets, with out the support of a proper CMS, have to be visible to the project.
Using typical inapp source control would/could mean that the coder would have to pull first, which could take up to 15 minuets, to just do a 30 second push. Adding to the problem that is how your main source control repro grows from a manageable and slick 50 gigs to a bloated 160 gigs.
So how did we land up solving our issues?
To solve things until something better comes along we broke things down to what is needed rather than trying to make things more convenient by having 3 repos based on the needs of the group.
Content SVN
We created a SVN repo just for art content and environment development that can be pushed and pulled to with out stepping on the toes of the coders.Source control is not even required because art content is art content and the only requirements is to be able to revert the SVN and because of it’s nature there is a ton of backups based on the number of devs mirroring the repo.
Code Git
All of our code stuff is managed through git as this is what git was designed to do. The fact that LFS was hot glued, patched on to the back end, the first place is a statement that the original design did not even account for large project development like video games. In this configuration the coders are happy as it’s business as usual and they can do their thing with out the need for the concerns of the content, big data dumps, and can easily be maintained. GIt lab and bitbuckets are now a usable resource.
Main Build SVN
The main build SVN is were code and content is consolidated to as to what is required by the game. Coders would update the build files and pull what they need from the content SVN and only what is required and use a build bot that will build all of the files into the working game and make it available for play testing. A tip consider adding Steam to the mix early. 
As disconnected as it might sound it works and with out a true definition of what is source control a simple “Hay Bob I’m working on such and such” gets the job done. After all it should be about keeping people working and not about having to steal locks all the time 