Well, here's the latest plan...
1. Use my Painless Battery Sw via a relay as planned... but with a 5 pin relay (one that has post 87 and 87a outputs) Where 87a is the default relay switch connection when NOT activated. 87A will provide the ground to the Painless Battery sw. The Viper Security has a -500mA output when ARMED.... and will drive this relay to the Batt Sw. and therefore disconnect ground by switching from 87A to 87 (87 will not be connected to anything). This way, if the Viper dies, I have ground to the Batt Sw by default, therefore, pwr to the car. I’ll add the toggle switch that came with the Batt Sw between the relay and the batt sw as designed. Again, another way I can kill the Batt sw.
2. Viper disconnect of Starter
3. Viper disconnect of MSD Ignition box.
I'll still install the back door, carry extra relays and several male-to-male 1/4" spade couplers to bypass the relays if all else fails.
The Viper 5901 also has a long range feature in that the LCD remote FOB has up to a mile range and will monitor the security system and let you know of any activity. I just received the VSM100 Viper Smart Start option that adds cell network connection so I can access/control via my iPhone. This way, I can monitor the car anywhere I have cell connection and not need the FOB (the iPhone will lock/unlock, receive alerts, etc). Obviously I won't use the remote start feature... not much use in a open Cobra .
And, yes, I know this is all an overkill, but I can't help myself.... I love "gizmos and gadets". Over engineering isn't bad, is it?

Mark