I can slap and pop reasonably well. I concentrated on having a nice fundamental technique all summer and can get a nice fat sound and some fast runs.

However, I'm terrible at incorporating the technique into creating my own slap/pop bass lines. Any tips on how to create my own stuff? Playing a line with fingers is easy, but making an original slap line dumbfounds me.

Great question!...here is one suggestion:
Try creating a bass line with finger style (you said this was no problem) Then figure out how to play it using slap techniques. You can "enhance" the bass line by using common slap sounds such as octaves and muted notes. The cool thing is that this method also makes you figure out how to not let technique hinder your playing and brings you closer to playing anything slap style that you can finger style.

I'll give it a try. thanks

You don't have to re-invent the wheel. Listen to the masters: Ray (of course), Larry Graham, Louis Johnson, Victor Wooten, Marcus Miller, Flea, and the many others...

Learn their lines and then add your own flavor. Have fun...