Sounds like a great spot for water intrusion and rust over time.That would be an easy project. Cut the hole for the projector in the bottom of the door panel, with the lens sitting flush against it or even recessed a little bit. I'm not sure where the door switch is, but you can tap in to that for power and ground.
Point well taken! My biggest concern would be the cutting - if you don't seal those raw edges, those will surely rust!No problems period. Tap the electric, cut the hole and make sure everything is sealed water tight. Magic!! These cars have water vents on the bottom of doors anyway to let out water that gets in through the exterior window trim. So you already have chances for moisture to come in anyway.
That's not a bad idea but I wonder if the lens would clear the door seal. Either way I think that would be the easiest way to mount it for sure.Isn't there enough flat bottom on the the bottom of the interior plastic door panel to recess it? Then no need to cut steel.