I just replaced several lights in my 3124KS with LED's. They are not cheap. I got the replacements from
www.superbrightleds.com
(1156-x45-T: 45HP-LED BA15S Tower Bulb) (Yellow)
There is very little difference between the LED and the original incandescent 1156 automotive bulb except in the current they draw. They are very easy to install.
Old 1156 = 1.4 amps @ 12 volts
1156 LED = 0.27 amps @ 12 volts
I'm very happy with them.
I also replaced the spots in the front of the TM with LED's (1156-x30: 30-LED BA15S bulb) (100 deg cool white) They are a little difficult to replace since they fit tightly in the socket.
If you have read the article in the trailer life, they are pushing the LED's.
Also, Look at
www.starlightsinc.com and
www.jirahled.com for fluorescent replacement bulbs.