Hi Guys,
I've seen H-18s rigged mostly with spinackers to the mast hounds as currently configured. You can fly the chute from a point higher on the mast but I would recommend two things:
1) Find and purchase a used "solid" aluminum mast. As you are not "class racing" with a spinacker this should not present a issue I would think.
2) NEVER EVER "dump" the mainsheet, you can "dump" the traveler but not the Main!!!! Go swimming/capsize instead, it will be much cheaper in the end. If you "dump" the main you run the risk of snapping the mast because the main and mainsheet are acting as a running backstay. And if you are using a comptip mast the higher the spinacker hounds the chances start to increase immencely!!!!
Good Luck
Harry