Solar Install on Roo 23SS roof

Thanks Don, you are 2 steps ahead of me, I was considering buying a cheaper PWM controller until I could get what I wanted, so you answered that before I had to ask (any MFG recommendations?). I'll give the 12V some thought, I have been happy with my Trojan's, and would ideally like to just add vs replacing...

Back to my OP- any ideas on roof construction for the 23SS? Or should I not bother looking for a joist, and just screw directly into the roof?

Marc