Best way to make mesh into 2d image for game texture

Hello,

I'm working on making a paintjob/skin for a truck in American Truck Simulator. The traditional method of doing this is using a 2d image editor to draw onto a provided template (typically generated by an export of the unwrapped UV layout for the truck's body mesh); however, this can sometimes be tricky due to the way the mesh unwraps.

The typical template

For example, if I make a straight-line stripe across the body and the side of the hood on this template, you would expect the stripe to angle down nicely on the hood, but instead it ends up strangely curved in-game. To try to get around this, I thought it would be both easier and more accurate to model a "stripe" in Blender, and use that stripe mesh to create the required 2d texture for the paintjob.

The modeled \"stripe\"

While it's easy to get the shape I want out of such a 3d "stripe," I'm having difficulty figuring out the best way to export that stripe into a 2d image with the correct mapping. My first thought was to Boolean intersect the stripe mesh with the truck mesh, effectively reducing the truck mesh to the stripe area, and then exporting the UV layout to overlay onto the template in my image editing software, but regardless of the resolution I can't seem to get it smooth - I always end up with jaggy, aliased edges. Similarly, I tried baking the intersected area, but the bake was jagged as well, even at 4096x4096 with 4x AA.

Is there a best way to make a nice, clean, smooth 2d image of the stripe, using the same UV layout as the truck, so that I can make a paintjob/skin texture with the stripe in the correct position?