The Harken Catalog is a great wish book and is also useful as a source of ideas for modifications and additions to Potters (and other boats). Once you have the modification in mind, it is a good idea to think, "How can I do this cheaper?" Particularly with the P-15, the rig is so small (the entire BOAT is so small) that the load on the components is little enough that cheaper and lighter weight hardware will do the job. Inevitably the vast majority of kits and gadgets in the catalogs are meant for much bigger boats than our Potters.
A case in point, I think, is a vang for the P-14/15---someone has just posted a question about that, I think. I believe that I was able to buy enough stuff to make one for about $25, considerably less than catalog listings that I've seen.
Regards
Tom Grimes
P-14 #363 Far horizon
Muncie, Indiana