it will also depend on which DT you are using, your post didnt indicate how old they were either.
I have some that are twenty plus years old and I have to be really careful with them especially on rough surfaces or corrugations, over details, etc. My newer ones seem to be fairly tough.
Also, you will need to use a dull #2 pencil or what I use which is a really cheap transfer stump that I got at Michaels or Hobby Lobby on clearance, it is a wooden dowel with two rods that have round balls at each end. Nice and smooth, and makes getting into crevices a bit easier while not poking thru the plastic as a pencil may.
It seems redundant, but the DT can be applied to clear decal film and applied that way, espcially if they are really fragmenting on you, just seal them with clear first so they dont wash away.
HTH
David
Build to please yourself, and don't worry about what others think!
TI 4019 Jolly Roger Squadron, 501st Legion