It’s a poor analogy, but imagine a public IP like a hotel, there can be lots of guests (clients) at this hotel. Hotel policy is they won’t let any outsiders in unless you know the room number (port) of the person you’re trying to reach.
Imagine you and a friend are staying in separate hotels and want to give each other copies of your favorite Linux .ISOs, but neither of you knows the other’s room number - you show up at the hotel and the front desk tells you to pound sand because you don’t have their room number.
As long as one of you knows the other’s room number though, you can meet.
Torrenting without port forwarding means you can only trade your favorite .ISOs with people who have port forwarding enabled (sharing their room number to the tracker), which makes you less effective of a seeder. Enabling port forwarding allows you to share with anyone (sharing your room number with the tracker).
https://www.reddit.com/r/VanLife/comments/1avrsbd/rooftop_solar_tracker/
Looks like someone out there had the same idea.
https://www.roboteos.com/shop
They’re currently selling a packaged system for ~$5k, which is a bit pricey, but maybe worth if you’re full time on the van life. Looks like you could probably fit 2 of these units on a typical roof, obstructions permitting. Alternatively you could do one tracker and one flat unit.
It looks like ground based 2-axis tracking systems can be found for ~$500-1k, you’d just need to bring your own expertise to mount it to the roof and program the controls yourself.
Semi-unrelated: others mentioned painting your van white (which you already have) but I’ll raise you one better - consider painting it with an IR-Emissive cooling paint, e.g., https://i2cool.com/
There’s unfortunately few products on the market at this time, but keep your eyes peeled.