No matter if your right or wrong, the bottom line is;
"His car his way."
Trashing him won't help and is extremely rude. Your way is not the only way even though you consider it the right & only way.
Express your opinion on how to do it and leave it. Trashing him, exclaiming it is a waste of time and repeatedly telling him what you think is right doesn't help the issue and only serves to make you look like an ***.
The best you have is to tell him; "Intold you so." When he comes back with a complaint.