Some things about doors....
In general... the latch assembly in Fiero is in kind of a bad place. Quite a bit of water can get to it even on cars with good dew wipes. This means it isn't dificult to get frozen out of the car. Mine did this just the other day when the lock arm on the latch froze. I was able to get in thru the other door but even the interior lock button on the frozen door was dificult to move. The key would have broken before the lock opened. I'm not sure electric locks would have opened.
My point is Normally it doesn't take a huge amount of force to work the latch. Don't count on Normal operation, especially in an old car.
They make kits specifically for this type project. Use them. Whatever they cost is worth it in terms of having reliable access.
If you are eliminating the deck lock, which I rally do not recomend... To prevent lockout when the battery is dead... find some place to craete an externally accessable accessory Positive terminal for the battery. Then you can connect jumpers w/o needing to get at the battery.
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Be alert. The world needs more lerts...
The Ogre's Fiero Cave (It's also at the top of every forum page...)