Tom
>> After spending several hours on the roof, prepping the base and looking for the cross-members, I finally gave up. The only cross-member I could find for sure was in the wrong place<<
Heat up the inside of your motorhome & wait for a dewy/wet morning, I'm sure you have lot's of those where you live<G>, the rafters should be outlined on your roof & you can mark the ends with a Sharpie pen for later install.