Winterpaw VRChat Masc Canine Latex Outfit & Hoods

To combine the latex texture in PS/GIMP you: 

1. Open the avatars original body *.png texture in GIMP/PS 
2. Go to the folder where you've exported the latex texture from the *.rar and drag that over to PS/GIMP until GIMP/PS opens, still hold unto the texture until you've brought your cursor over to the main texture (cursor should have a PLUS on it (at least in GIMP) and release. This should now create a new layer where the latex material is on top of the original avatar texture: Export as PNG, preferable under a new name so it doesn't overwrite the original!

To combine the latex body mesh parts with the avatar involves Appending in Blender:

In short, you bring the latex outfit meshes to the original avatar *.blend file, so to begin first open the avatars original *.blend file. Then save that as a copy (just in case).

A tutorial on how to Append in blender: 

The actual instructions on the posted tutorial on how to Append starts at 1:30. In this case when you've selected the intended *.blend file, only bring what's in the Objects folder.

When appending rigged meshes in this case, it will always bring its armature, thus creating a copy of it. So, with the original avatar *.blend file you now append from the latex outfit *.blend file its parts (Hoods, back zipper, nulges, etc.) But, since they have their own armature you'll need to reassign them to the avatars own armature.

To do this, you select the intended mesh to reassign, let's start with the back zipper. If you can't see it such as if the avatar is in the way you can rotate your view in blender by holding the middle-mouse-button. Selected meshes/objects are haloed in orange, so make sure the zipper is displayed as such. Now with the zipper selected, you'll go to the little blue wrench icon to the right side of Blender, this is the Modifiers tab where you should find the Armature modifier.

On the Armature modifier is a field titled Object. Since the Appending brought a copy of the original Armature, it has been renamed "Armature.001", you'll want to re-assign it to "Armature". Now do the same to the rest of the latex outfits meshes Except the zipper handles and padlock as that's using its own armature (done this way in case people want to give them dynamic bones).

Now since the armatures are being reassigned, if you want the zipper handles and padlocks to be included you're going to have to Parent the zipper handles bones to the avatars Armatures Chest bone. Instructions on how to Parent objects or bones to another bone can be read here: http://dense13.com/post/blender-parent-object-to-bone/

The instructions doesn't mention how actually to go into Pose Mode with an Armature, but I'll tell you! With the armature selected you go to the upper-left corner of Blender you'll see a field reading "Object Mode", click that and you'll get a drop-down list of actions, the lowermost option reads "Pose Mode".

When all's done, you should be ready to export FBX, make sure to un-tick "Add Leaf Bones" in the Armature section of the FBX export window to avoid making unnecessary extra bones.

As for combining it in Unity, let alone making a unitypackage, you may have to refer to tutorials on that as I've never even set foot on VRChat. Resonite is easier, just import the *.blend file that you've just worked so hard on!

Good luck!