How about those LED strip people use on pickups? They're usually mounted between the lower part of the tailgate and rear bumper. The ones I've seen light red when braking and amber when signaling to turn.
I can't seem to find one that is 18", and it needs to be a single row or it won't mount correctly, or at least how i want to mount them. I did find one that i thought was going to work, but surprise surprise, it ended up being a chinease special that didn't match the description. Only 1 showed up, and it progressive lights for the turn signal, so it doesn't work correctly. Was supposed to be 2 18" LED light strips for a left and right set up, but such is life. Still looking when i have time, i know i should be able to find something....
West Marine has a very good selection. Styles and lengths.....
I'll check 'em out. Might try and dig through superbrightLEDs as well and see if they have one that will work. But essentially i want a truck tailgate light bar, but 18" and red/red/amber with the reds in 2 differnt brightness for running lights vs stop.
If push comes to shove, i know i can get some red/red strips pretty easily. But if i do that i will want to replace the tail lights, and the ones i really like have been out of stock in the style i like. Just going to be one of those years i think. lol