I am a Trane dealer since 1992, I was a Carrier dealer as well for a year.(you can make the assumption)The xl 15i is a big waste of money. The seacoast kit is usually used under the extended warranty. It is required within a mile from the coast with the extended warranty. The XB is the best bang for the buck. Have your dealer put the 10 year part warranty on the XB, it is very inexpensive. Have a load calculation done on your home, like Dave said above.
22' Sterling all black hull
Mercury 300 XS