If you flash the coroplast with propane torch CA will hold it very well. Just pass the torch over the plastic and you will see it takes some of the shine off. A lighter turned up on high might work but will take a bit longer. Practice on a scrap piece. If it warps slightly let it cool a minute and it will straighten out again.
Go to SPADtothebone.com and look at building tips.
good luck. I learned to fly on a SPAD. Very forgiving planes.