Which more rat vehicles can they add?

So I love from time to time to play the rattiest vehicles in the game, however not many nations have them so my question to you are. How many more can they realistically add? What tree can get the rattiest vehicle?

My favorite is the 20mm Wiesel. You can be the best scout in the game due to thermals and insane mobility. You can also assassinate SPAA/SAMs in the enemy spawn.