When I have an area like that to do I dry fit everything and then when I do the layup I'll do it on a piece of wax paper in the reverse order. Then I'll have a piece of plywood ready, 1/4" would do with the appropriate size sticks to prop it up in place. Sometimes even a hot melt glue gun will be helpful to hold things in place.
The key to success with an operation like this is rehearsal otherwise it can turn into an ugly mess really fast lol
