As other here have mentioned - call Winnebago Technical service. Not only will they try and give you very helpful advice and information about your rig, but they do have, and will email to you, many other PDF technical drawings for any model they manufactured.
About 1 1/2 years ago I wanted to install an additional MaxxAir fan in the BR, over the bed to help provide some cooling there on hot summer nights. Like you I was very concerned about location of roof braces, roof A/C ducting and roof wiring, so did not want to simply start cutting.
So called Winnebago, got some helpful advice, and was immediately emailed separate drawings showing locations of all the above on my specific model. So knowing this I was then able to determine where I could cut the 14 x 14" hole in the roof without doing any damage to anything else. Then installed this new fan - no problem - and been happy with it ever since.
This is one of the reasons I love Winnebago - their customer support. In case you did not know they also offer a lot of technical bulletins and drawings which you can download directly from their website. I downloaded a full parts catalogue, some technical service bulletins, and electrical diagrams in this way. Love it!
In contrast - To help a friend out with their Thor Class A a couple of years ago we needed some technical info on his model. Accessed the Thor website - found nothing so called into their headquarters. They were not at all helpful, and even made us feel foolish for thinking that their units would ever break or that we could even work on them as ignorant owners. They simply said to call a dealer. So we did, and the dealer was not at all helpful as they did not want to waste their time on answering technical questions - they only wanted to take a parts order or have us bring the RV into them for service.
So again - that bad experience with Thor only proved how valuable Winnebago customer support is. Hope that Winnebago never forgets that!
Rick & Barb
2005 Winnebago Adventurer 37b