Well the problem is that whenever you add custom assets it will increase the size package. The maps that manage to stay under 100MB are the ones with little to no custom assets at all. ( Specifically textures and sounds are the big ones here )
The added textures to the latest release are completely in tandem size wise with tripwire assets and are graphic in nature, meaning I cannot use clever shader tricks & UV mapping to reuse 1 texture like crazy. I use appropriate compression and masks to get the most out of the textures I've included so there is really nothing I can do.
On top of that, unreal packages are not really setup to be all that compressed, because it needs to load fast. That is why the compressed download is only 60MB but the "uncompressed" package is around 280MB.
It would be better for tripwire to allow compressed redirects, BUT upon reading the documentation on the wiki they have already solved this problem in the form of the steam workshop. So the map creator is supposed to upload it the workshop and I presume that the client will automatically fetch it from the workshop when joining a server.
I don't know if this system is in place yet, but tripwire is working on it and will update the documentation closer to release as they said so themselves in the grindhouse deadline delay info.
I'm planning to put the next release on the workshop, so that would solve the problem.
Having said all that, there are a few assets from Tripwire like the TVs and commercial signage that don't have their UVs setup for optimal reuse, where the contents and outer border/shell share the same UV channel. So every texture for that has about 30% wasted space when changing content. But optimising that would only yield you somewhat better resolution here and there as going one mip down would make it too blurry.
Hope that clears things up
It's not a solution for this current release as much as it is an explanation for why it is that way.
