In this one steam guide you'll find two video guides i hade made about skyboxes.
One dedicated to making HDR skyboxes, another on the 3D Skybox aspects.
Both will teach you everything you need to know about skyboxes.

3D Skyboxes are difficult to align if you don't know some neat hacks.
But fret not, this video explains it all.

All you need is Hammer++[ficool2.github.io]

I made a python script that automates the tedious part of HDR Skyboxes.
All you need to do is render the skybox from blender, drag it onto two tools, and you are done.

Here is a list of things you need:

My Prefab[github.com]
MareTF[github.com]
Blender[www.blender.org]
Python[www.python.org]
FFMPEG can be installed throuhg CMD prompt, by tiping

Join the "Dead 4 Mods" Discord Server[discord.gg] if you need help.
Use the dedicated mapping/modding channel to ask questions.
If you join and immediately DM me, i'll ignore you.

I have my own Discord Server[discord.gg] if you'd like to hop in and chat.
I sometimes post WIP images of what i'm doing, but it's mostly memes.
Support me via Ko-Fi[ko-fi.com] or Paypal[paypal.me], so i can make more free prefabs like this.