If you are using Half-Life 2 then the materials have to be in the half life materials folder. If they are in Gmod materials folder, it will not show up in HLMW. (At least for me this is the case). Try copying the materials to both places, and check if that solves your issue, then you can experiment where you should have the materials located for preview.

Here is a quick visual example:
http://imgur.com/a/Pe3HG

You have to create a collision object from priitives. This means you have to create the collision from rectangles and cubes. Each of the collision object has to be separate, and you ahve to export them as a group. After that, specify this mesh as the collision object, and use the $concave command in your QC to tell the compiler that it is hollow.

What is the issue you are facing? Please describe in detail the phrase "doesn't work".

Hiya,
I am a modeler, I use Blender for 3D printing and game assets, as well as scenes. I used to create Gmod gamemodes, but got bored of it :) Currently I am working with UE4 on a project with a team.

Hiya,
Oh, It is the MV logo I made for some dude in Blender :D How peculiar.
Anyhow.
When you model something in blender, there is the material part on the right side. The textures in Gmod have to have the same name as the material name in blender. So if you have a material in blender called Material.001 then Garry's Mod will try to find the Material.001 named vmt. So name your materials inside Blender properly. In your file, the material is called mvglogo_material, so name your vmt to mvglogo_material.
The mvlogo_collision is only needed when you wish to have another type of collision. Otherwise the compiler will make a collision model based on your mesh. For example if you model a house, and wish to step inside it, you need to create separate collision mesh for it. In your case, since its just a plate, you do not need it.

Regards,
Papi

Blender is a great way to start, It is free, and elaborate. Starting to model is a huge task, and requires a lot of effort in pushing yourself over the initial ragequits when something doesnt work like you want it to. Another tip is to forget about modeling cool stuff at first. Always look at reference images, as they have details you might not see first, or forget they exist. Start simple. There are some tutorials on cgcookie (https://cgcookie.com/learn-blender/) that might help you get started.
Some things you might consider modeling for starters is as follows:
-a key (understanding extrude tool and vertex manipulation)
-a keypad (understanding bevel and inset tools)
-a computer screen (understanding mirror modifier)

It might sound very stupid but modeling simple things can be very hard. You may try your luck at modeling rocks. It does sound weird, but it can teach you a lot of important ways to pay attention to detail, and how to manipulate your model.
One thing to keep in mind: try to use only quads (quad is a face that has 4 vertices, so basically a rectangle). It will be easier for you to oversee the model.
You may argue that the game engine changes every quad into triangles, which is true, but if you model with triangles and ngons (polygons that has more than 4 vertices) then the model itself will be harder to manipulate for you.

There is a youtube tutorial for blender basics from one of the CGcookie artists:
https://www.youtube.com/watch?v=zOvawDOWqC4

Hope I could help,
Happy Blending!

You should put garrysmod folder inside your addon folder so it goes addon/garrysmod/models and addon/garrysmod/materials.
Hope it helps!

Hi,
I am using Crowbar 0.19.0.0, and model viewer still works. I am using Half-Life 2 as the engine.