changing the meshes/body

ok so many people know about my 4runner mod i am trying to get going in game however i am stuck every where. the main question is how can i take the roamer body and everything else and change the meshes into my model. ive exported my model and changed the objects names and meshed in blender to say exactly what the roamer.dae file says but it ether makes the roamer disappear or just crash the game i have the original roamer untouched, i made a separate file in game for the roamer.) i dont expect this to be answered but i rather ask then not at all.

 

Warning: this post contains a lot of text which may be overwhelming.
To quote Hitchhikers Guide to the Galaxy: Don't Panic!

First you need to create a clone of the Roamer. Create a folder in the mods folder named: unpacked. Create a new folder within the unpacked folder with the name of your mod. Within that folder create a new folder named: vehicles. Within the vehicles folder create a new folder with the name of your mod. Copy all of the Roamer files into this folder. (mods/unpacked/mod_name/vehicles/mod_name/roamer files) Find the roamer.JBEAM among the files you just copied. Rename it to mod_name.JBEAM. Open that file in a text editing program. At the top of the file find where it says "name":"roamer". Change roamer to your mod name. (Same as the folders) To test if it worked, start BeamNG and open the vehicle selector. There should now be two roamers.
Rename roamer.DAE to roamer.dae (it may already be lowercase) This isn't necessary, but can make your life easier.

Next you need to prepare the mesh. Make sure all parts are named the same as the corresponding parts on the roamer, which you said you already did. In order to make the mesh visible it needs a texture. The following is a quick temporary solution. Each part in the mesh needs a material. Import the official roamer.dae file into a new different blender project. Look at the material names of the different parts. For now just look at the body panels. Most of the panels will have a material name of either roamer or roamer_body. ( I think it's just roamer. I'm doing this by memory, I may be wrong. ) Go back to your 4Runner model, and assign every part in the model a material with the same name as the roamer body's material. Switch to the UV editor in blender. Import the roamer's .dds file for the body. ( It should be called roamer.dds or roamer_body.dds located among files you copied into the mods folder. This picture represents some of the textures that are mapped to the roamer.) Select a part of the model, and hit tab to enter edit mode. Hit the a key to select all faces. UV unwrap the mesh make sure the dds file you imported is selected in the uv editor. You should now see a bunch of polygons in the center of the image. These polygons represent the polygons on your mesh. Move the mouse over the uv image with the polygons. You can scale them by hitting the s key and move them by hitting the g key. ( same as modeling the mesh ) Position and scale the polygons so they are over and within the roamer's hood pictured in the uv image. Repeat for every component.

Now all you need to do is export the mesh. Switch from the UV editor back to the Default view. Exit edit mode. Make sure to apply the location, rotation, and scale of every component. Select every component, and export the model in the .dae format. Make sure it's named roamed.dae ( you will be replacing/overwriting the .dae file in the clone you created in the mods folder. ) Also, make sure you apply all modifiers of the model and only export the selected meshes. ( these are options to the left of the screen when exporting) Replace the .dae file in the clone you created with the one you just created.

Restart BeamNG, cross your fingers, and spawn the roamer that doesn't have the BeamNG logo next to its name. You should now see your mesh.

I wrote this from memory, so please forgive me if I missed anything.
I hope you find some of this helpful.
Let me know if you need me to explain anything I wrote.
Good luck!
--- Post updated ---
I realize that I may not have explained this very well.
I might make a thread to explain this in a little bit simpler way with pictures.

 

Here, this may be a little easier to understand:
https://beamng.com/threads/tutorial-testing-your-mesh-on-an-existing-vehicles-jbeam.41130/

 

You literally just killed my brain but i tried it and it worked

 

I'm glad it worked for you!
Sorry for killing your brain. I realized my answer wasn't easy to follow. That's why I created a separate tutorial.