Hi there,
First, you have to download the 'scs extractor' utility. You can find it here, at racedepartment, in the Mods section of the ETS2 forum (so, you are pretty close to that section, aren't you?).
Then go to the root folder of ETS2 and save 'def.scs' to an other location, to keep your installation clear. After that you have to put the downloaded scs_extractor.exe into the same folder.
The next step is easy: just drag and drop the 'def.scs' file over the ''scs_extractor.exe'. A black command window will appear. Make sure you wait until the window is disappeared by itself, don't close it manually. When it's closed it means that the util has finished with extraction of the moddable content.
You will see quite a few new folders. Look for the one called 'camera', then 'units'. Inside the 'units' folder you can see a couple of .sii files. You can edit them simply with notepad. You need the ones starting with 'interior'. Open 'interior_daf_xf.sii' for instance, and you will see a value called 'camera_fov: 77'. Change it to your liking. It's a try and miss process, really.
After changing all interior camera files you have to inject these values back into the game. Create a .zip document including all the subfolders inside the 'def1 folder (excluding 'def' itself), so the structure of the zip file has to look like this: camera/units/all the edited interior files (8 pieces, if you alter the cameras of all trucks). You can name the .zip as you want, it doesn't matter.
After creating this file, change its extension from.zip to .scs, and that's it! You've just created a mod for ETS2. Now, you have to copy that file into MyDocuments/Euro Truck Simulator 2/mod folder.
I hope, I was clear enough?
Cheers,
Vilmos