What is "MAT"? Possibly you have a trigger that is destroying them? Or you've mismatched some fields:
You must check that certain fields match each other. Important ones for destructables are:
Art -- Fixed Rotation: -1 (always -1 for random facing, otherwise it would look lame as fixed 270 degrees facing)
Art -- Model File -- Variations: MUST MATCH THE DOODAD'S VARIATIONS
Pathing -- Pathing Texture: Should match the doodad's pathing but it's up to you
Combat -- Targeted As: Your preference, though I put Rocks, Vines, etc. as "Terrain"
Also, make sure you don't create destructables with a non-existent variation with triggers (say, your Trees have 7 variations but you've put in GetRandomInt(1, 10) and it returns 10).
There was also some field that blocked vision but I can't remember which one... Might be problematic if you create Shrub off of Trees and you suddenly notice the shrub blocks vision.. ;D