I'll make a few comments about the fan install I did today -- just the stuff that may be different, or insightful, or annoying. It's already been covered by others, with lots of photos:
The most unique thing about my install may be that I did the entire thing from inside the van. I only had to climb a ladder on the outside, to do the final placement of the MaxxFan into the installed flange**. If you're skinny, you may be able to pull this off, as well. I could not think of a good way to get high enough and stable enough on the medium roof van to work on the exterior. And, I think the unsupported roof areas will distort or bend if you look at them wrong.
My goal was to try to maintain the roof's curve by adding side shims cut from vinyl brick molding. I did trial and error on the subtle angle, until I got it right. The scales on my saws are not very expensive or precise, but, the angle is 2 1/2 to 3 degrees. See photos.
I cut the hole with a jigsaw, yes, from the inside. Instead of drilling corner holes, I drilled 5 closely spaced holes in the middle of each side. I cut between the holes with a Dremel with metal cutting wheel. Then, I was able to cut from the middle, to the corners with the clunky jigsaw. This was a bit awkward doing the transverse cuts, having to hand-support one edge of the saw's foot, while riding the tape-protected cross-beam on the other edge. I had to finish off 1/2 inch in 4 places, with a handle mounted hack saw blade.
Like others, I clamped all of the parts together to drill holes. I had already fit some wood for the underside, which will maintain the spacing under the ceiling liner, and the MaxxFan trim piece will screw into the wood. I had put some cross-grooves in the upper surface of the wood pieces, so that on final assembly, I could apply some 3M 5200 and get better adhesion, to have permanent pieces, there. Not that I ever want to remove the MaxxFan flange, but, if I did, I would not have to deal with the wooden spacer blocks, again. tthrsn has good info on using 5200 to attach wood to metal
I used butyl tape for the initial seal of all exterior parts to one another, and to the roof. I think I had 5 layers of tape at the widest gaps at the sides of the front and rear edges, near the vinyl side spacers. One photos shows the butyl material after I had trimmed it with a plastic picnic knife. There's no pic, but, I later applied Dicor 501 caulk (which one MaxxAir video, I think, favored) all around, and over the screw heads.
That's all the good stuff.
Here's the bad stuff about the install.
I try to do things right, so I will be satisfied when I look at them, and be proud to show them off to others. Sometimes **** happens. I'll blame Ford for this one, although, under more ideal circumstances (more forethought, less pressure to get work done while it's not "supposed" to rain, more available assistance, maybe more experience, etc), I could have done better.
"What, what, tell us what you're talking about!"
Well, my vinyl side spacers are nice and perfect, and the fan sits perfectly on the roof panel. BUT, the roof panel does not sit perfectly on the roof crossbeam supports! Id say it's about 1/8 inch higher on one side, and, if you're looking for it in the interior, you can notice this by the thickness of the anti-vibration foam between the parts. So, the roof is lopsided, but would not normally be noticed. Now, from the rear, particularly with the vent open, there's a noticeable tilt to the fan assembly, in relation to the van (of course lopsided roof line is not visible). I'm really pissed about it. Pissed at Ford, and at myself. I could have compensated for this by adjusting the thicknesses of the vinyl side spacers.
** My statement about only using the ladder on the exterior one time is not quite true. I had to take a detour after getting the cutting and filing done, to vacuum up metal filings on the roof. This was a bad scene. You have LESS time than you think, to get all that stuff. We had some humidity today, and some of the smaller, barely visible bits started to attach firmly to the paint finish. And, the filings and chips vibrated and moved on down the grooves in the van top, to near the front of the roof. I could not vacuum them while standing on my ladder, up through the 14x14 inch hole. Had to move around the exterior, climbing the ladder with big shop vac in hand, awkwardly vacuuming everywhere. I still don't think I got it all. And, the places where the microbits clung on, I'm going to re-visit after I drive into town to get a mild scrub sponge, which I'll try using with denatured alcohol, or maybe just car wash soap.
Whether cutting from inside or from outside, it would be best to have another person on the outside, chasing the cut with a vacuum brush-fitting.