[crunch]

If your exploders are models, you need to include a player clip or just a clip as part of the exploder to keep players from walking through them.
Or, if you are replacing a good model with a destroyed model, if it's relatively in the same place, the clip does not need to be part of the exploder or the exploder_smashed script_objects. It will remain after the explosion.

Your exploder_fx should be made from the 'no draw' texture. This is a non-solid texture that doesn't get drawn in the game, making it perfect for explosion effects.

And just as a precaution, tick the 'no marks' flag in the surface inspector for your trigger. This should keep you from getting floating bullet holes after the trigger is hit.

I don't know however if you actually want them solid or not?
If they are actual brushes, they should be solid unless you don't want them to be. Unless you used "no draw" instead of "caulk".