I was having the same issue (not using Warp Stabilizer either). My prproj file ballooned from 100MB to 1GB in a matter of days, making it almost impossible to open. I got my file down to a workable 200MB by doing the following: [Warning: be careful, this could be destructive if you don't work from a duplicate. Never do this to your original project file]
1. Duplicate your project file.
2. Open it with a text editor (right click "open with", choose "other", then choose TextEdit on a MAC. I think on windows it is ctrl+shift right click, then choose notepad or wordpad.)
3. Look for 2 pieces of code that look like these:
<PreviewItem Index="7363" ObjectRef="344492"/>
and...
<PreviewMediaSerializer ObjectID="345345" ClassID="a3cdecce-0e72-4ad3-8b59-aa53b1b54070" Version="1">
<Media ObjectURef="b3a4e115-add5-4cfb-9164-dcfec34cf94e"/>
<ID>7c708748-9a78-1855-cc1d-d88f00000053</ID>
<End>23587781817600</End>
<Start>23172474124800</Start>
</PreviewMediaSerializer>
There will be many, many instances of these. (Mine had literally Millions of entries of each snippet.) With every iteration, the entries double in size. My first pieces of each of these referenced roughly 50,000 pieces of media. The next 100K, then 200K, etc.
4. Starting at the last instance of each of these massive chunks of code; highlight them and delete. Work your way backwards (or up, as it were) and delete each progressive chunk of entries. Being careful to not remove ALL of the entries, just the later duplicates.
I suspect there are other areas that can be removed safely, but this is all I did. It made the project much smaller and I was able to successfully open it. I've been working out of it for the last 5 days and everything is still fine. The filesize has actually gone down subsequently.
Hopefully this is helpful. It might be good to save a version after every time you delete a chunk, that way if you get to a point where the project won't open, you can just try the previous saved version and so forth. I'm not saying this is the best way, just what I did to get my project back.
