For the me game crashes with certain guns if you click on a certain mod when trying to modify the weapon. A few weapons that do this that I can remember off the top of my head are:
Car-4 when clicking on Stealth Barrel
One of the AK guns when clicking on one of its mods, cant remember which
The Compact-5 sub-machine gun has one of it's mods crashing the game too.
Also unlocking the mods makes all the new DLC items invisible in the mods list, and you cannot modify the scope reticle anymore when you have unlocked the mods using the trainer.
can you purchase the items, then close the game. then restart the game without the trainer and THEN craft without problems? the trainer is mainly mostly effective to allow you to see the items and buy them.
obviously we are trying to minimize the trainer UNLOCKING or DISPLAYING items that a user who DIDNT PAY FOR IT needs to actually purchase DLC content to see.
best,
Cal