Update for anyone still looking for this. I went for simple, and matching my priorities: water intrusion, freezing temperatures and power loss (which can cause the other two).
All from Amazon: HomeSitter ($80), Xlink Bluetooth gateway ($40), old cellphone ($0), plus a battery-backed power source for the Xlink (UPS or 12v to 9v adapter). I also pay $10/month for "monitoring", which is the cost of the extra cell phone line for the boat.
If power is out for more than an hour, or there is water in the bilge or if the temperature drops below 45, or the batteries are weak, I get a phone call on my cell phone, home and work until I fix it or disable the callback.
Not perfect, but good.