After a trillion hours of research, I finally started learning how things work, I used to do mods for skyrim and I used blender and 3ds max alot, although, doing a bit of research for this game, I found out that the .mesh file comes from something called "Ogre 3D" which from that point, things gets a bit less complicated to understand, I can't show you or give you tutorials, but I will however, help you in the process of understanding all of this and hopefully i'm not too late, either way, assuming I am or not, i'll share my findings
Possible programs/ways to make meshes (custom models) for kenshi:
1.Blender 2.49b (Make sure you have python 2.6.6 or 2.6.4 installed as the Ogre3D exporter AND importer requires it *note that blender might be the only program that accepts imported .mesh files so if you want to import vanilla files from kenshi, then this program is for you)
2.milkshape 3D (I use 1.7.10 *note that this is a payed program but probably the best tool for making low polygon meshes which is perfect for a game like kenshi, it also has an addon that allows you to EXPORT any models you made as .mesh, sadly you cannot import .mesh files)
3.3DS max (I use 2012 STUDENT version)
4.Maya (Honestly, I never layed my hands on maya)
5.Ogre Command-line Tools (using version 1.7.2 *this is also important as you will need to convert the vanilla meshes from kenshi to .xml)
if you have one of those programs, you might find yourself going back and fourth exporting/importing the meshes on one program to another, but before you do anything, get these tools/addons and apply them on one of those programs I listed above:
http://www.ogre3d.org/download/tools
this is an example of a vanilla .mesh file I got working, played around with it by adding different shapes and such.
