Playing bass under Travis Picking

I enjoy travis picking finger style and am learning bass, but apart from pedaling the root, what's the scope with the bass when the guitar thumbing out a bassline too?

I would go with listening to songs in that style and go from there. If all else fails you can use the old standby, as long as it sounds good.

I think the notion is that the bass and the guitar are going to interfere with each other because they are both playing bass lines.... but that gets solved with nothing more than EQ and/or arrangement.
 
SOLVE WITH EQ
When the guitar is solo, the low end may be left natural, or even boosted a little to bring out the bass notes. This creates a very full sound. When a bass is introduced the guitar will often have an HPF applied (I'd start around 120hz, and likely go higher as needed) to make some space for the bass. The guitar will still be chugging away and you don't know that is isn't "as big" because the low end has shifted to the bass, yet you still hear the guitars low notes cleanly.
 
SOLVE WITH ARRANGEMENT
You just have to make sure the two lines work together. There are no rules as long as it sounds good. The only thing you really want to avoid (unless you are after the sound) are two very dissonant notes being played at the same moment.
 

Guitarpima
I would go with listening to songs in that style and go from there. If all else fails you can use the old standby, as long as it sounds good.

 
+1

I'm no guru by any means....but I agree that "messing with it " and practicing to find what works in a tune is the best thing that will get ya where ya aiming for.   I also agree with Coda's points   ;o)