"Steel garage door 5x3 (powered)" I CANNOT get two sensors (outside and inside) linked to the door at the same time.

You have to connect them in series.

PowerSource -> Sensor -> Sensor -> Door

Originally posted by Ghost:

Originally posted by Prismatic Platypus: But then don't both sensors need to be triggered for this to work?

No, either sensor being triggered will trigger the door.

More specifically, When two sensors are wired in sequence, IE
power - everything else - sensor 1 - sensor 2 - object(s) to be affected by sensor
they function as an OR gate, where both sensors receive power and can distribute that power down the line to the objects to be affected

However, If you wire it like this:
power - everything else - sensor - literally anything, even a relay - sensor - object(s) to be affected by sensor
Then they function as an ordered AND gate, Where sensor 1 must be tripped for sensor 2 to even receive power, and then sensor 2 must be tripped while it still has power, meaning BOTH must be active at once and in sequence to trigger the object to be triggered.