I don't think the environment should negatively affect Alabama much, at least in terms of crowd noise. They have certainly played worse in general on the road under DeBoer, but as you noted they have played in two far more hostile environments so that part isn't a real concern. It's probably more just Missouri being comfortable at home vs. potentially looking shaky on the road that's to Missouri's advantage.Regarding home field advantage for Missouri, I think that's overblown. They have the least intimidating stadium outside of Vandy. Bama as we noted have played in two very hostile environments already. Bama face perhaps the most hostile environment I've seen at Fsu in recent memories. It was so loud and crazy, I knew it would affect our offense. In Athens, Kirby never lost a night at home and was 33 -0 in Sanford stadium. It didn't bother Bama one bit, heck I think the team thrive on it! The biggest advantage I believe for Missouri is that is an early game and Missouri had a bye to work on their game plan.
It is still set up the way Missouri would want it to be, as you noted early game @ home, also a revenge game, coming off a bye, also coming off a tough game for Alabama. Some similarities to Vandy last year. The team just needs to show up and handle business though, as long as the team that played FSU doesn't show up I think Alabama should be fine.