Thanks for the response. I did it as you say for my Arctic Fox, but I would rather find the trusses. Allow me to explain why. And part of this reason has to do with wanting to use strut channels, for the problem I'm about to describe would be more prone if trusses are missed.
I've one not so obvious reason to want to find the trusses. If you place a screw about midway between the trusses, it will appear to be tightly fastened. However, if you step on the roof adjacent to the screw the roof would try to good give a little. I've seen this give before. This slight deflection would put stress on the screws holding power by pushing the roof away from the mounts. Over time this could become a problem and maybe introduce a leak. The roof at the trusses would have no give.
However, on my Fox I did not find trusses and I mounted them using tilt kits. I never had a problem with it, and it held perfectly for four years.
bcrvman, I've done as you said and it worked. I'm just looking to do it a little better. Thanks again for your response.