I got you skin and icon in game.
Change "model_default_steam" to "model_default"
Change "icon_default_steam" to "icon_default"
Note I'm, pretty sure it has to be the way I changed it for any skin. If it is RED or BLUE skins that the skin file would say "model_red" or "model_blue" same for icons. As "icon_red" or "icon_blue."
Also you do not have to use TGA you can save skins in Microsoft paint as JPG or PhotoShop as JPG. I always do.
Also I uploaded you icon to Photoshop and saved it as "Baseline Optimized" with a quality of 9 and as a JPG file. I don't think it matters if it's JPG or TGA I alwasy do JPG.
P.S. Don't worry about the stormtrooper caps. That is just the textures for what you see in dismemberment. They do not have to be in the PK3 with the model.
Every cock fights best on his own dunghill.