Help with UV Unwrap on object with large amount of messy vertices

I am working with a model of a car that was 3d scanned. This resulted in tons of vertices. I have gone through several tutorials on UV unwrapping, learned about seams, converting to quads, and several methods. I’m having no luck creating a UV map that is usable. I’ve tried to set seams horizontally accross the nose, to no avail. It’s difficult because there is no straight line through any part of the model.

I’d like to be able to apply designs as a paint job to the car. Please see the attached images for examples.

Does anyone have any idea how I could get a workable UV map? Or is there an alternate method I could use to get paint designs onto the car. Your input would be greatly appreciated.

try the decimate modifier to reduce the amount of faces/verticles …

I’d expect that modifier will give a poor result in this kind of model if you want to reduce the number of polygons to give a reasonable unwrap as you want to keep the smooth lines of the car.
You’ll get a much better result if you retopologise your mesh