mine are in the sail panels as my tweeters need to be aimed directly on axis with the listener, but in these trucks competition has proven that tweeters in the pillars aimed directly across at each other is essentially the best setup. This will vary some per tweeter and listener/tuning but should yield good results.
Ultimately what I suggest is that you cut some long speaker wire and use some double sided tape, or hot glue, or some temporary form to mount the tweeters in various potential positions then spend some quality time and some critical listening.
One issue that can arise with mounting seperate tweeters comes with path lengths and the difference in distance from the mid speaker and it's paired tweeter to the listeners ear. If the separation is too great your ear will pick up on the separation between the high frequencies and the low frequencies.
I used hot glue as you can see and it worked great, easily peeled off the plastic when I was done with it and held strong for weeks under moderate temperatures. Final product was beefed up and fiberglassed.
