I recently purchased UAVcast-Pro for my rpi 3 companion computer. It is a simple 4G LTE package that allows multiple GCS telemtry feeds and one live video feed (developer said the rpi was the bottleneck to not allowing more than 1 live video feed) all based on Zerotier VPN which allows for static IP address assigned to both GCS and RPI no matter the location. I am in no way affiliated with this company but had the pleasure of getting plenty of help from the developer via chat on discord. it is actually quite simple to setup (especially if I was able to) and have included a video of my simple setup using a pixhawk cube running arduplane 3.9.4 to a raspberry pi 3 on Verizon Wireless in the US. The hardest part was trying to get an honest answer out of Verizon if my 4G LTE dongle would work on their network!! UAVcast-Pro noncommercial is the same product as the commercial, as I have been told commercial allows some company based GUI and few other customization, the code for the working parts of this are the same commercial vs. non-commercial.
This is also the video I used to setup my VPN netowork UAVcast-Pro Zerotier setup
Video to setup RPI with UAVcast file