Original Instructions (this will require Decal Prop Fix, no longer recommended):

Install ModTools

Import your decal prop in the asset editor. You can use this box mesh[www.dropbox.com] as a template (example textures included). Scale the fbx box mesh if you want a different size than 8x8m.

In the asset editor after importing your prop, open the ModTools console with F7. In the command line in the bottom of the console, paste the decal conversion script[gist.github.com]

Before you press the "Run" button, edit the values of the script:

In line 2, specify the size of the decal (e.g. (16,4,16,0) for a 16x16m decal). The second parameter (4) is the max height of the decal, which is important for steep terrain. The entered size must match the x,y,z size of your mesh!

In line 5, change the tiling of the decal (e.g. (3,0,3,0) for 3 texture repetitions in both directions).

Options: In line 50, change the priority of the asset in the prop menu.

Now press the "Run" button. Your box prop will be converted into a decal. You will see success messages in the console.

Do not touch the colour variations, do not try to change the colours! The script saves the extra data in the colour variation fields!

Now save your prop

List the mod as a dependency when you upload to the workshop!