Undercarriage repair failing -- Any suggestions?

A plastic panel that runs under the passenger side of the Prius is coming loose. I posted about it back in 2010, but did not get much of a response, so I eventually just went ahead and came up with my own repair idea.

Here is my somewhat awful photo that I took back then, I snapped the photo adjacent to the jack point behind the front passenger side tire. You can see where the panel is sagging down and dirt has packed in...later, the sag got much worse and leaves, gravel, dirt (all wet and mucky) all packed in between the plastic and the steel underbody.

K&KinOregon | Flickr

So the repair lasted a few years, but I notice it has come loose again. Any new suggestions, or should I just clean-up the muck and fix it as I did before.

Here is what I did to the panel before:

There are three main nuts -- a 10 mm at the front, a 10mm at rear and a 12mm in the center of the panel. As well as two plastic nuts on diagonal corners. I was not able to remove the rear plastic clip so was not able to take panel completely off.

But, I cleaned as best I could, dried out the "compartment" with hairdryer, used just about all my nail polish remover to clean the edge of plastic and underside of car and then spread a film of GE clear silicone on the edge of the panel that seats against the underbody of car. I then replaced all the bolts and used two jacks and wood blocks to assure that the panel (which was still hanging down at front corner) was pressed firmly against car.

Waited two days and removed jacks and blocks and panel seems secure (drove it about 50 miles). However, there are still a few spots where debris could enter (too large to fill with silcone).

NOW:
Earlier this week a noticed a strip of silicone hanging down, so I pulled it off and looked at the panel. It is sagging along the front corner again. I figure if no one has any great ideas, it is back to the silicone and acetone.

 

Thanks all for the support and suggestions!

I am still somewhat disabled from a stupid ice injury in January and I am not wanting to really get into this, since it does not seem critical at the moment.

I imagine by the end of the month, the weather will be better and I will be capable of getting back under the car and seeing what is actually going on. I don't remember much about why, or what I could not take off when I originally did this. But, it seems like silicone will be the solution once again.

If I run into any real issues, you all will "hear" about it.
kris

 

While I do understand the logic of "bending" the plastic, as I recollect, it is fairly stiff, somewhat like the inside plastic trim panels. I don't think applying heat from a hairdryer is going to make it "bendable," but if anyone has any suggestions on how to do, I am open for suggestions.