DARCO is a "think plastic tarp material"... I'd be very concerned with spraying anything on that material and hoping that it won't tear or droop. The DARCO is not attached to the wheelwell, just "laid over it and secured at the perimeter".. That means, to me, that if you spray a thicker coating of anything on the DARCO, if the plastic tarp tears, so does the coating.
So, for me, the solution was to just leave the DARCO in place and install an "independent" covering that didn't rely on the DARCO for any strength or attachment security.
To me, relying on the DARCO is like draping a blue poly tarp over your house, then rolling on a new tar paper roof. As soon as the blue poly tarp slides, so goes the tar paper....
Or maybe, applying a coat of quality paint over some "blistering" wall paper. The paint may stick super well, but as soon as the wall paper falls off the sheetrock, so does the paint...… YMMV
2015 F250 6.7l 4x4
2014 Cougar X Lite 27RKS