I also, was but making an attempt at humor. '...Being Served?' is well known to fans of British humor this side of the pond.
No offense taken, friend.
I am concerned - certainly, the 'broken tile' only becomes an issue when it rains - and surely you do not propose to fix it in the rain? Defer, defer.
Speaking more Aerodynamically, foam board aka 'foam core' can readily be made waterproof with an application of epoxy or epoxy paint. Works quite well. Paper element absorbs the resin, stays smooth (thin applications are best).
I am making 'compartments' in the radiator area after the example being discussed, using 'foam core/foam board'. I have a 'NACA duct' type arrangement on the lower front deflector, pushing air up in front of the radiator, already, this 'compartment' will make that more efficient, so I think, we will see. NACA ducting is not really intended for applications where a 'diffused' air stream is used, but it seems it works well, and is perhaps cleaner than a conventional 'leading edge duct'. Looks neat, anyway.
Nice thread, an idea I had not really thought much on.
Will