To actually make a cubemap using Nvidia's Photoshop .dds tools, you have to do the following:
-split the cubemap image into 6 equal, square parts
-piece these pieces together, side by side, in a single layer.
	-An easy way to achieve this is to resize the image you want to use to a height of either 128, 256, or 512, and
	 a length of 6x that (768, 1536, 3072 respectively.)
-save the image using the following settings in Nvidia's plugin:
	-DTX5		ARGB	8 bpp | interpolated alpha
	-Cube Map
	-No MIP maps
-your cubemap will be split up and saved with the correct settings.

To apply these cubemaps to custom weapons in game, you must add the following to a material_config file:
-Your render_template must contain CUBE_ENVIRONMENT_MAPPING somewhere, or the game will not look for a cubemap.
-A line below your texture maps that looks like this:
	<reflection_texture type="cubemap" file="environments/mods/cubemaps/shovel"/>
		with the path being the path to your custom cubemap.