For what it's worth, I have never succeeded in showing a model in the model viewer with textures, even when I know for certain the textures are in the right place.

You're probably better off just spawning the model ingame to view it there, either by making a quick test map in hammer or using a console command like spawning a prop_dynamic or somesuch.

yeah i did that, and garry's mod's model viewer works and shows the textures, so I guess half life 2's model viewer is just broken for some reason?

Could be. I had tried HL2's and NMRIH's in the past, never tried GMod's.

Hopefully someone with more experience with the model viewer comes along.

I know this is pretty old by forum standards, but I would presume you two are still interested:

I narrowed down (but not confirmed) about a year ago that it's something to do with how HLMV parses or mounts the gameinfo.txt in regards to specifically the custom folder, if so likely on account of its wildcard

To circumvent the issue, you can add a line to the gameinfo's SearchPaths which explicitly mounts to any folder of your choice (even outside the game files) so long as you use an absolute path (ie: the full "C:\etc\etc"), and in that location you can store your model and mats like it was the game files itself and it'll work both in HLMV and in-game

I even created a batch file to automate populating the folder when compiled, and figured I'd upload it for yall with some helpful comments to show you how to set it up for yourselves, available here[gist.github.com]