Re: Roof deck structure question
Keep in mind that every hole you put in your roof presents a possible entry for rain to enter. If you are to use L brackets, you must seal the screw area well. It is not so severe if you have a curved roof. If your roof is flat (like on the Dodge class C that I had) the water will pond.
The nice thing about a curved roof is that the water sheds off the roof. Nevertheless, if you use L brackets, first squirt some sealant into the screw hole for the L brackets, and then seal the top of the screw with some rubberized sealant. Once you put your decking boards on, you will not be able to access the framing very easily.
There are MANY methods of putting a deck on a bus. This is just one method that I did. I used wood because I am not much of a metal fabricator. Actually, there are probably many better ideas than mine. However, my method DID work.
Before you settle on a design, it would be prudent of you to research all the methods that the members on this site have employed.