Prius 2008 gas door not closing

welcome! the rain won't hurt any thing. i would start by examining the locking mechanism. have someone pull the handle while you study the catch at the door. there is a part on the body that should slide in and out as they pull and release the handle or button, i forget if the '08 is mechanical or electric. if it's not sliding, it might just need lube. or it is possible that the cable became detached.

 

When you push the door closed does it go in all the way (to position that it would normally stay)?
What does the gas door release leaver feel?
Loose and doesn’t even really go down by itself?

Your second picture doesn’t show area under the gas door rear the gas cap. There should be a pin that locks the door shut.

If the pin doesn’t stick out try to push the pin in a bit. If it then jumps out, test that the pin goes in when you pull the release leaver. If it does then use some oil on it and it’s fixed.

If the pin sticks out, test that it goes in when you pull the release leaver. If it doesn’t go in when pulling the leaver then there’s something broken which needs to be replaced.

 

Maybe try a little silicone spray. Very sparingly, just trickle a drop into the mechanism, try to avoid overspray onto paint because it makes repainting difficult. Silicone lube is very clean, not sticky, attracting grit.

 

The gas doors on these cars must have a high failure rate or I am just lucky enough to own 2 out of 2 Prii that have this problem. It could be a regional issue as well as I am dealing with long winters and many sub-zero nights, road salt, sand, etc, etc...

Not sure if this will help you but the problem with both gas doors in my case seemed to lie in the "hinge" mechanism which over time distorted and became subject to rust. Lubricating the hinge did neither helped nor prolonged the integrity of the gas door. It had been difficult to close for a while prior to that event although it did close. The door of my '05 (255,000mi) eventually fell off as I was driving down the highway but luckily, I heard the bang and was able to retrieve it with only a few chips on the edge where the door hit the pavement. For now, the door remains off.

The 2008 had an issue when I first purchased it used in 2013. I realigned the door and it has been fine ever since that time but I suspect that within a few years, the hinge will eventually fail and break off. (currently 123,0000mi).

I notice that your gas door is missing a bit of paint on the outer panel edge (hinge side). It looks as though the door is hitting and rubbing against the frame when it is fully opened. If so, the door is not properly aligned...

 

like your duct tape idea. maybe velcro.