I have led lights under my hood, I went the route of adding a controller which I wired to the positive lead and found a nice ground spot close by. I used velcro and zip ties to attach the controller to the side of the fusebox. I used 2 different colors of lights and have had them on for over 6 months now, and have not had any issues with sunlight/ heat from the engine etc.... I had purchased a spool of LED from E Bay and the other color I had to pay retail prices (PeP Boys) as I was having a difficult time finding it anywhere.
This is the controller I bought, it is a Logisys Corp. 4 Zone Multi Mode 12V Remote Control (RM08)
3 of my friends have had similar setups in there Challenger/ Chargers for over a year and have not had any lights burn out and no fading or other issues described. We all used the normal tape which comes with the lights as well as using some zip ties when possible.... everything sticking very well for all of us.
I kind of like the idea of the remote controller as it lets me do so many different things with the lights instead of just an on and off.....
good luck with whatever you decide.