OK, here are the latest pics. It's all worked out and in place. I still need to caulk/seal it all up and put in the final hardware. Found the 4" stainless bolts I've been looking for yesterday.
Fantastic fan in it's final fitting. MUCH straighter than the factory fan.
I'm using metal to reinforce the edges around the fan. Stiffens things up, takes the stress off the fiberglass at the bolts, helps take the sag out of the roof.
Another corner brace.
Corner brace and over the braces on the rear side of the fan is a 1/8" thick aluminium bar that goes across the entire middle part of the roof. This really helps reduce the roof sag!
And this is the corner where the roof sag is worst and where the added aluminium bar really works it's magic. There are two bolts through the roof and the bar, this is where the sag is mostly taken out.
Here is the Fantastic Fan in it's final configuration. I haven't sealed it up and bolted it with it's final (stainless) hardware. But it all fits great. I will be replacing the plastic border with wood moldings. There are wood molding on the escape
hatch and I'll be replacing that too so they have matching molding stained to match the Brazilian Cherry Allure flooring.
Another view, you can see how much "lift" my custom risers give. The knob is at least 1/2" above the ceiling level, no more bumped head like I got constantly with the factory fan switches. Actually, I think I'll be spending a lot of time standing under this fan. The only place in the trailer I can stand up straight and stretch!
Here you can see the bolts that pull the aluminum roof brace snug up the the roof. Bye bye sagging, bendable roof!!!! Well, there's still a sag, but it's minimal and you don't notice it from inside or outside even unless you'll looking for it.
For a fan/vent replacement this was horribly complex and expensive, but I'm VERY pleased with it. The added roof strength will give peace of mind and it's SO much prettier! Not to mention the fan works SO much better than that grotty old factory fan.