How do I create window collision models?

I'm wondering how I can create window collision models for more complicated objects, such as a windshield (or really anything that isn't 99% flat). Certainly, I've had success with creating collision models for flat windows, as I was able to create that whole partition collision thing and add windows to Trevor's Bodhi. I've also been able to reliably create collision models for small solid objects to block bullets, but I suppose that isn't really relevant here. 

My problem lies with the non-flat windows. Right now, I'm trying to add collisions to the windows of the Frontier in my PPD pack, but it just doesn't work. I've been trying the following, which works for flat windows and metal/car body (with modifications):

1. Add Crash to the window material's user-defined options if not already
2. Create a box primitive sized to the window
3. Convert it to collision object, append [COL], and nest it under the window object
4. In the collision model's properties,
   1. Check Flat shaded
   2. Uncheck Tangents and Primary Color
   3. Change UV Channels to 0
   4. Add Crash to the user-defined properties
5. In polygon mode,
   1. Delete the sides of the box, leaving only the front and back
   2. Change External State to 122/121/120 depending on the window
   3. Change GTA V > Options and check See through, No ragdoll, and Shot through FX
   4. Change Group/Type to VEHICLES and CAR_GLASS_STRONG/MEDIUM/WEAK
6. In vertex mode, weld each edge

This doesn't work. All it does is result in the bullets passing straight through the glass.

Interestingly, changing External State to 116 and changing GTA V > Options accordingly to make it behave like metal makes it work: The bullets then do not pass through the window and instead hit it (although without bullet holes).

Any thoughts? Thanks.

Edited August 8, 20223 yr by Tactical Donut