I've done just about everything written on this forum to get my mod (some skins and new weapons) working with a custom campaign.
That includes:
- Reading the sticky
- Downloading someone else's mod (he said his campaign was working) and comparing the code to mine
- Moving the whole scripts folder to my mod's folder
And yet nothing.
So what's the deal? Some people had trouble but they got it working in the end. Too bad they never told us how, they just added "EDIT: Got it working!" to their posts. Sad sad sad...

How is it not working? Is it not appearing in the custom campaign menu or is it that nothing happens when you try to start it, or does it crash?

A few things to check for clues where things are going wrong are the logs at %appdata%\Running with rifles, namely rwr_game.log and metagame.log. You can also post them up on e.g. pastebin and share the links, maybe we can figure it out together.

No crashing, it allows me to select it on the menu but when I get into it, it just shows vanilla assets.

Sounds like it is probably starting the vanilla campaign. How does your %appdata%\Running with rifles\metagame.log look like after you try to start the custom campaign?