So When Do I really Need A New Alt. Belt 08 RT?

I have 24,000 miles on my 08 RT. The serpentine belt in my Ford F-150 lasted well over 100,000 miles. You guys have the answer.
Help? When is a good time to replace it and is it easy?
I am a pretty handy guy with lots of tools.

It's easy to do by yourself. If I were you I would replace it around 30K, or at least buy one and have it with you.

I have about 40k miles on mine. I am going to replace it but since I have not, I can't say what shape it is in. It is easy to replace and there are tricks on this forum (like plastic soda bottles) to protect the belt when it is slipping onto the pulley.

I would say, or actually, I do say it is best to replace it before it breaks.
We had someone up north who had over 50k on theirs. However, he in saying so to us obviously jinxed himself and would not have made it back to Washington without it breaking.
He was carrying one, so we helped him replace it.
The belt looked ok. Do not go by looks. They can look ok, ... and break.
They break because of age, and stress and other factors, not that they no longer look good.
So let me say, get your new one, learn how to put it on, then do it at 30k. Or when it breaks.
It is easy to replace, with a certain technique. Without just the right finesse, it can be very difficult and nasty.
dc