I hear the frustration in your post. Let me try to clarify a couple of things.
Virtually anything will work. The question is, how well?
It is best to have insulators at the ends of an end-fed antenna (like a backstay). However, a fiberglass hull is a pretty good insulator for the lower end, so on most boats you can, indeed, attach the feed wire (GTO-15) from the tuner directly to the backstay. You can even do this UNDER the deck to avoid having to put a hole in the deck. HOWEVER, the usual reason for installing a lower backstay insulator is to avoid potential RF burns. When you transmit, some pretty high voltages can be present on the antenna, especially at the ends. If someone were to grab the lower end of the antenna while you were transmitting, he/she could get an RF burn. If this isn't likely or possible on your boat, then go ahead and forget the lower insulator.
An upper insulator is a good idea; otherwise, your backstay is likely electrically connected to the mast and the rest of the standing rigging. This could limit its effectiveness as a radiator.
One thing which works very well is to install a separate backstay-like antenna off to one side. I've done this on my boat, and it's worked well for 18 years now. Every bit as effective as a standard insulated backstay, and you don't have to break up the integrity of the main backstay by installing insulators.
I built mine from s/s lifeline. You can see a pic of the lower end at: http://gallery.wdsg.com/Misc-Stuff-S...y2_0130?full=1
Also, there's lots of discussion about "anternative backstay antennas" on the SSCA board and others.
Don't forget the RF ground....that's VERY important, too.