It might come as no surprise that radio signals don’t like to penetrate metals. What was surprising is how little it takes to completely annihilate a common wifi signal. Shut the door from the inside of the trailer and you are essentially sitting in a faraday cage. Even with a relatively powerful router (Netgear R7000 Nighhawk), not more than 20 meters away from the antennas, communication was essentially impossible.
Leaving the door open only several centimeters I was able to get a good signal with a speeds of at least 54Mbits. Once the door is shut none of my devices, be it laptop or mobile phone, was able to connect or even pick up my SSID. I really did not expect the thin aluminum sheets to block out signals to this extend.
To solve this problem I would need to mount a repeater or wireless bridge that has an antenna on the outside, and one on the inside of the trailer if I want to have Wifi there as well.
Bridges and repeaters are relatively cheap these days and so are external antennas. I have never had to mount radio equipment that has to resist the elements but apparently there are plenty of options.
I used a TP link station with two external antennas. I removed one of the factory antennas and hooked up the new outdoor antenna.
Reception inside before:
With new Antenna:
Conclusion: for around 50$ this was well worth the money. I can now shut the door enjoy my privacy and still have a high speed internet connection. (insert relevant youporn joke here). The antenna works great and surely gives the mobile hacker-space a more techie look. Also during traveling I will be able to use this as a repeater for open wifi access points.