First things first, here's a disclaimer for you:
Nice. Now that we've got that out of the way, welcome to my skin testing guide! I decided to make this because there used to be a guide from KikET for this, but it is now outdated and some people couldn't understand the text. It helped me create this guide, though, so you should go and give him a big hug.

So enjoy this freeride to amazing skin screenshots, and I hope you'll learn everything you need to know about testing your skins in-game!

First things first, you need to get the Unity version currently used by Unturned. This can be found in the bottom of the "Creating" section of Nelson's general Workshop guide. As I'm writing this, the current version is 5.5.0f3.

After this, go to the Unity download page and scroll down to "Older versions of Unity" and click it (or click this link)[unity3d.com]. Here, find the matching editor version and download Unity Editor for your operating system. Run the installer and follow the given instructions. (You only need to install Unity Editor, everything else is optional.)

After the installation is complete, open up Unity and create a new project. (You need to log in, but you probably should be able to create a free account and use Unity Personal to follow this guide.) Next, go to the Unturned files and navigate to Bundles/Sources/Tools, where you will find BundleTool.cs. Drag and drop this file to your Unity editor.

Now that you've got Unity up and running with Nelson's BundleTool, you need to create the materials. Drag and drop all the textures you made in the skinning process into the Unity editor. Now create a new material named "skin_primary". Now assign the albedo (and any other material components you might have made for your skin, like emission) to the material.

If you're making the skin for a melee weapon, you should be good to go, but for guns you probably want to add attachment skins. I got this information from KikET's guide, so I cannot guarantee that this is how it's done, but I trust him in this, as the rest of the guide was extremely helpful. Anyway, you need to make a "skin_secondary_#" for every attachment you want a skin for, with # being replaced with that attachment's item ID. And if I understood correctly, by making a material called "skin_tertiary", that material goes onto every attachment you didn't make a specific skin for, so it should just be a pattern of some sort.


The last thing to do in Unity is to export the asset bundle. Navigate to Window>Bundle Tool from the top bar. This should open a very empty looking "Bundle Tool" window with a "Grab" button. Now select your materials from the Project menu and click that "Grab" button. You should see all your textures and materials show up in the Bundle Tool, along with the shaders your materials use (probably Standard). Now click the Bundle button and save the asset bundle wherever you like, as long as you'll be able to find it.

Now that you've got your asset bundle, you need to put it into the Unturned files and configure Unturned to think that one of the items in your inventory is actually your skin.

Let's start off with inserting the asset bundle in the correct place. Go to your Unturned files and navigate to Bundles/Skins. Here you will see weapon names. Notice that some weapons have a different code name than the name they have in-game. If I remember correctly, you should know this from when you got the weapon model for the UV map to start the skinning. Go to your item's folder and create a new folder inside it with the name of your skin without spaces (preferably replace them with underscores). Now you need a .dat file of the same weapon for your skin. Go to another skin's folder (it should be of the same weapon, but I think other weapons that are the same type (melee/ranged) should also work in case no skins already exist for your weapon for some reason) and copy its .dat file into your skin's folder. Also move the asset bundle you created with Unity to the folder. Rename both the bundle file and .dat file to the same name as your folder.

Now you need to edit the .dat file. Open it up with your favorite text editor. Not sure if this is required with skins, but firstly add this line in the file:
Then change the ID to whatever you like, as long as it's a number between 2001–65535 (inclusive).

The last thing you do is you need to change the data of one of the skins in your inventory to replace it with your skin. Once again, the disclaimer:
This is the part where carefulness is key, because YOU WILL GET VAC BANNED for not following EVERY SINGLE STEP.

First of all, go to the root directory of your Unturned files and CREATE A BACKUP OF YOUR EconInfo.json file. This is the pesky little thing we'll be poking with our modifications. Open EconInfo.json with a text editor. Find an item you have in your inventory. For me, an example is Flektarn Yuri. Double check that you have the backup before changing anything. Now change the "item_id" value to the item ID of the weapon your skin is for. Then change the value of "item_skin" to the ID you gave your skin in its .dat file. Triple check your backup and save the file.


Indeed it is! Now launch Unturned and go to your inventory. Find an item with no icon and with the name of the skin you just replaced.


Again, you won't see an icon for it, but you can equip it and see the skin.


To test it, GO TO A SINGLEPLAYER WORLD with cheats on and use @give <item_id> to give yourself the item.

Enjoy your own skin in your hands, finally physically in your reach! After you're done admiring it, have all dem screenshots and want to go back to multiplayer, REPLACE EconInfo.json WITH THE BACKUP YOU MADE. This will return the inventory item back to the weapon it used to be and prevent any future VAC bans. You can leave the files in Bundles/Skins be, in case you want to test the skin again in the future.

Thank you for your time and thank you for reading my guide!