All of mine are rigid LED strips with zip-tie mounting.
On the sides of the car, I tucked my rigid LED kit under the plastic trim, and the light shines at a good angle down and toward the outside of the vehicle. I had originally mounted the LEDs to the bottom of the plastic trim, but they were visible below the car. Now they are out of sight.
In the front, I just drilled some small holes in the splash shield, and supported the LED strip at the ends and the middle with zip ties. If you're planning to use adhesive LEDs, a couple zip ties might still be worth adding.
I didn't do the back of the car. I put my 4th LED strip in the upper grille (and added a splitter and 5th LED strip for the lower grille).
It's been 4 months and I've had no issues, except for the time I forgot they were on and drove it somewhere. People kept pulling up next to me on the freeway and I had no clue why.
I want to do the wheel wells.