I find propper doesn't work for me on anything but Source SDK in the default half-life 2 configuration (with the requisite edits to make propper work at all). Plus that way it's easier to keep track of your custom models.
I can...but why not just use studiomdl? It comes with the Source SDK and you can just drag-and-drop your files onto it.
These are for HL2DM, right?
Sorry, as I've never mapped for HL2DM I'm having a bit of difficulty getting the authoring tools for it to work properly. They will be done soon.
I don't have HL2, I just got Deathmatch with Portal: The First Slice. Tbh I've never even played it.
Will compiling for Portal work, then? I think I can do that.