I've had several friends go through in-vitro. My wife performs IUI. What I can tell you is that you'll forget everything you're going through now as soon as it takes. And it will almost certainly take. And it will be worth it.
You can minimize rot by using plastic or mason block. You can also take comfort in the fact that if you build it right, you can fix it. My father-in-law's greenhouse is 40 years old; I helped him replace some panels and the footers when it was 37. Keep us posted.