Smaller fan than Fan-Tastic?

I was planning to install a Fan-Tastic 4000 fan in the roof of my Tin Tent.
I measured the trailer, and I have less than 12" between roof ribs, so a 14" square Fan-Tastic won't fit.
I need something that's integrated, has a dome opening, and is assured to be weatherproof. I'm very nervous about cutting a hole in the aluminum roof, and I have no confidence in my ability to fabricate something that is weather proof.
As usual, thanks in advance to a great bunch of folks.
<Chas>
I measured the trailer, and I have less than 12" between roof ribs, so a 14" square Fan-Tastic won't fit.
I need something that's integrated, has a dome opening, and is assured to be weatherproof. I'm very nervous about cutting a hole in the aluminum roof, and I have no confidence in my ability to fabricate something that is weather proof.
As usual, thanks in advance to a great bunch of folks.
<Chas>