MikeAqua:

 

I've been doing a few trip-tips this summer.  I'm FODMAP so I make my own dry rub and leave it on under clingfilm overnight, in the wine fridge so it doesn't get too cold.

 

To cook I sear the meat and indirect cook fat side up at about 110*C with pohutukawa and apple wood chips.  I pull it out when the core temp is 47*C and rest well covered before serving.  Everyone says it's amazing.

 

Hmm, love me some tri-tip.  As a suggestion, you could try reverse searing it.  Pretty much do what you said above, but sear last, rather than first.  The smoke flavour can get in a bit better if not seared first.  Also, if you rest the meat between the slow cook and the sear, then you can cut and serve straight after coming off the BBQ - while still sizzling on the outside.  There's lots of info online about reverse-searing.