Adrian
I had a set of HPC coated pipes on a nother vehicle and stones (small) did not worry them.
Don't get the pipes coated by Jethot in Castlemaine. My coating from them is a mess. I went for Jethot as they were closer to me thinking it was a similiar coating.
They totally stuffed my pipes including the inner fibreglass. The coating as peeled off on all welds and up to 10mm either side of a weld etc. etc.
Just my $.02 worth on coatings..
Bernie