Great questions, Mark! I just wish I had better answers-- I'm just making this up as I go along. ;-) In fact, I just went back to see the photos to remember exactly how I trussed those birds. So I'm no expert, but I can tell you what motivates my setup and trussing.
re: trussing. I'm trying to keep the dark meat nice and tight to protect the white meat, and also trying to keep the whole bird from flopping around on the forks too much. So I kinda modify my classic trussing method by first running the string around the spit to kinda pull the legs down a bit, then wrapping around the ends of the drumsticks once, then passing the string by the sides of the body to tuck in both the thighs and the wings, then just tying the whole thing off to the spit at the head end.
re: heat. Yep, gummi is right on about my reasoning. I have done a lot of rotis cooks with a full basket on either side of the kettle, which brings the whole kettle up to a good roasting temp and gets the chicken done just a bit slower than a traditional non-rotis cook. And the meat is super-juicy for sure, but the skin isn't too crisp. Then I noticed that someone here (Brian, maybe?) said he always does rotis cooking with the heat on one side, so I thought I'd try it (I also has a friend who hand-turns a whole lamb on a rotis over an open pit every Easter, and he builds the fire on just one side). But the bigger factor is something you can see if you take a look at the video link that gummi posted earlier in this thread: the traditional pollo a la brassa method has the birds on spits, but that whole spit assembly also *rotates* over the coals, giving each bird a close pass over some high radiant heat every minute or so. So I was trying to approximate that, without having the fire right under the bird the whole time (which I can only imagine would expose the chicken to a lot of flare-ups).
So. In an effort to get some more radiant heat, I elevated the coal baskets to sit right next to the birds. Which does help with flavor and crisp skin, but also takes a bit longer. Or at least it seems to-- I've only tried it this way twice now. The lid therm on my old SS says the kettle is as hot as ever, but for some reason the whole process seems to take more like 90 minutes. Again, your mileage may vary and I might be totally wrong about this (like gummi, it seems to me that the ambient temp inside the kettle should be just as hot, since there are the same number of coals inside there, but my experience hasn't borne that out just yet).
Give it a try in whatever way seems sensible to you, and let us know how it worked! I'm sure we're all eager to learn from one another, and as much as I love Peruvian chicken, I can't eat it more than once a week. ;-)