Mesh Decal System

I've been trying to design a decal system which will conform or create a source mesh (decal) to a destination mesh(s) (world geometry). The effect I want to acheive can be found in this blog: how-to-project-decals

I understand all the concepts behind this, but not so much how to actually implement this. I've been looking through books and on the web for almost a week now, and can't find any useful resources to help explain the implementation side. I'm not looking for code per se (although its more than welcome), just a walkthrough of the implementation steps.

What I have done is use a bounding box, a simple box collider as a trigger, to check for collisions with meshes (on specific layers), and determine which triangles on the mesh intersect or are contained by the bounding box. However, my implementation of that is cumbersome at best, and does not even attempt to clip the decal to fit inside the box.

Any help, pointers, or resources anyone can give me on this will be greatly appreciated. Thanks in advance!