Yes, it well melt. Keep away from exhaust. It is very difficult to rip. Even if you start a cut with a boxcutter it is almost impossible to get it to rip. It is fairly rigid in one direction but bends easier in the other, same as cardboard.
not only will coroplast melt, it can catch fire in contact with hot metal.
this link tells exciting adventure of an EV owner whose coroplast belly pan caught fire when a small, hot piece of metal fell onto it after his controller failed. (this link is a repost from another thread here...)
Yes, I tried to catch it on fire before I installed it. After holding a flame to it for about 7 seconds, it finally caught. If you let it go without a draft, it will continue to burn slowly, but not like wildfire. It quite easy to blow out, easier than paper or a rag on fire.
For those who are concerned, coroplast is available in a fireproof formulation. But I imagine that it would very difficult to find. You might have to buy a large qty.
Just a note about the wind. Since I am on the highway with cars passing by, I am benefitting from all the air that is being displaced by the other vehicles which my ASI shows - 10 to 20MPH compared to the speedo. So I really never have a headwind as long as others are driving faster. My speed on that stretch is 45-55 MPH. What did have a detrimental effect on rolling resistance was the wet roads. All I need is a dry day with temps in the 60's and I should be good for 65MPG.
I am glad that I am inspiring others. That is the whole point in sharing techniques and experiences with others via gassavers. I know that SVOboy is working diligently to get the CX tranny. That is the only thing that stands between me and 70 MPG.
Oh, and another note. Last fall in similar temps and on the exact same route, I was seeing 67-70MPG in the Prius.