Since you are locking your game to 2018 tech, you cannot use modern mods. Here are the best mods that worked natively with 1.31:
Since the game is currently on much newer versions (like 1.51 or higher), here is how you can access the older 1.31 version or a physical/paper map for it: 1. How to Download Version 1.31 (Steam) If you own the game on American Truck Simulator 1.31 Download
The is not for everyone. If you want the latest trucks, maps, and multiplayer, stay on the current version. However, if you are a mod collector, a retro-gamer, or someone running ATS on a decade-old PC, 1.31 offers a rock-solid, nostalgic experience that captures the spirit of ATS before the era of massive DLC expansions. Since you are locking your game to 2018