Hey Mark,
1.) If you want to trailer up and do Channel Islands Harbor to Frenchies Cove on Anacapa, it's a short 12nm. Yes, there is a shipping lane to cross, but I've done this a number of times, and it's a really straight forward crossing if we go in sane (Read: not santa ana) conditions. Further, since the wind doesnt really pick up till 10 anyway, there's plenty of excuses for a leasurely start ;) (you are looking at sailing, not just rowing... right?)
Furthermore, I can brign along a sat phone, handheld vhf, and some friends that promise to come get us if we manage to miss the broadside of an island, without needing to resort to bothering the coasties (which can cost well more than any of these boats)
2.) If you want a hand at any point with the building, or just someone to kvetch at about the process, give me a call, I'll come down and buy you a beer to find out about your build out to date ;)
As for the modifications,
I would think any of the crossbraces under the seats would hold a harness fine, especially if you attached something like a chainplate to distrubute the load On my Josie, I had a line running up either side of the mast, from bow to stern, and would hook into that, which gave me the ability to move around on the boat without unclipping. Since my jib was hanked on, this was necessary for coming back in and taking everything down. This worked out really well for me, but is probably overkill on the dory.
Regarding the scuppers, the problem as I see it (once again, disclaimer; armchair boat design with 0 experience or knowledge here) is that as soon as those sails go up, you're putting the boat on her side, which means the scuppers are going to become a liability, or am I misunderstanding the idea?
It sounds to me like by pouring the floatation what youre really trying to do is eat up interior volume, so the boat can't flood. If that's the case, I'm not sure the dory is really a great starting point. Half of the appeal is the shear volume and displacement of the thing. It sounds like you're trying to build something that has more of a pedgree with things like the laser II.
Oddly enough, I have friends who have made these crossings on Lasers, and had no problems. They're unsinkable and really fun to sail fast, but that's not what this type of boat is going to be.
Either way, all my internet babbel is nothing compared to building and testing, (or the internet babbel of people who actually know what they're doing)
I am still pretty sure the Dory would be fine if you were to time your crossing correctly.
Anyway, enough of this post. If you want a hand with any of your work, or merely want to swap ideas, hit me up and I'll swing down to SD to lend a hand and hear a story. :)
-- James