How do you get the tyvek, or house wrap, to stick to the metal? Seems like a huge issue down the road if you spray the foam to the tyvek. I'm guessing that they want the tyvek installed before the metal goes on? Wrap the framing, then install the siding? None of this makes any sense.
Closed cell foam is used for boat docks. Closed cell foam is water proof. Closed cell foam sticks to everything it is sprayed to with zero openings. Not only does it give you a very high R value, it also stops wind and any potential leaks. If you can afford it, nothing else comes close to closed cell foam.
I think the Morton guy was mistaken and I would push the issue with them on this. Talk to somebody else if you are going to buy from Morton.
If you use open cell foam, there has to be some sort of barrier between the foam and the siding or roofing. It will rot out OSB and plywood if it's applied directly to those materials. It will rust out metal if it's applied directly to metal siding or roofing. Open cell foam hold moisture. Open cell foam will become wet just from humidity over time. Open cell foam never dries out once it gets wet. It is a lot cheaper, but it causes so many issues that it should only be used when everything is done specifically for it's use. I would never use it for anything, but I have read up on their websites on how it's supposed to be applied.
I had a client that wanted to buy and $800,000 home a couple years ago. She is a widow with the money to pay cash and this was just to live closer to her friends. She also has a very large house on the lake. She hired me to spend the day with her looking at the house and give her my opinion on what it would change a few things and make any repairs that where needed. The house was only 2 years old and the shingles where already falling apart. At first glance, the roof looked like it had been there 30 years. Rock was coming off the shingles, the corners where curling up and there was fungus darkening the roof. Inside the attic, there was 2 feet of open cell foam sprayed directly on the OSB roof decking. I pulled a little away to show her the damage, and the OSB was coming apart with mold growing on it. That house is still for sale, and the price is now a lot lower, but nobody is looking at it because of how bad that roof looks for an almost new house.