READ UPDATE AT END! In this video I show you how I built a water resistant truck generator to recharge my truck camper. It has 1500 watts of power and cost less than $250 to build.

Here are the parts I used:

1500 watt inverter
https://www.amazon.com/gp/product/B07...

Anderson Connectors
https://www.amazon.com/gp/product/B08...

2" Soffit Vent
https://www.homedepot.com/p/MasterFl...

4 Gauge Copper Wire
https://www.amazon.com/gp/product/B01...

Recycle Bin
https://www.staples.com/BrightonProf...

Cable Glands
https://www.amazon.com/gp/product/B01...

UPDATE: I tested this setup when my battery was at 40% and a on a sunny day. It worked great. It failed when I really needed it. It was raining. My battery was at 20%. I plugged in my truck generator, started my truck, plugged in the camper, and all the inverter did was beep. I suspect it couldn't handle the current draw when the battery was so low, and without the help of solar. I have since given up on this setup and am working on a DC to DC charging setup. If it works, I'll post a video.