I have recently started using
Paint Shop, which was added to the CSP.
Install it from the App Shelf in the in-game menu.
To increase the resolution of the skin to 4K, open Paintshop.lua in assettocorsa\apps\lua\Paintshop and change 2048 to 4096 on lines 16 and 33.
(I don't know if this is the right way, but it works for me)
Tutorial Video
Skins I have created (probably to be released next week)
View attachment 1387406View attachment 1387407
There are other add-ons that make it easier to do 3D painting in Blender.
LiveryHelper
Makes creating, editing and customizing car liveries much easier
extensions.blender.org