Shipping will be expensive as a result of the size of the pieces, last person I checked for it was over $60 to ship to Michigan. Not sure if PA would more or less.
The cap just presses in by friction. Mine are still going strong after 8000 miles, highway and some off-road. The inside edge is pretty thin after trimming and has more flex.
You need to buy the RokBlokz with the cutouts then modify the cutout to fit the extended rails. The rails go through the cutout. The other option would be to cut the front of the rails back then you could get the ones without the cutout.