Had a similar situation a couple decades ago that blew up in my face. Here are the countermeasures I should have insisted upon:
1. No deal is too good to walk away from. As soon as I smelled something, I should've said, "Thanks but no thanks."
2. You run a straight Delaware C corporation, not an LLC. If there's preferred stock the investor gets none of it. Use a boilerplate vesting schedule that lets you cut the investor loose if they turn toxic.
3. You retain access to the corporate checkbook. If investor balks, run away from the deal screaming.
4. If your investor has a change of heart (or health event, or divorce, or drug problem) in the next 9 months, it will be harder to raise money without his full buy-in than without his involvement at all. "Why isn't so-and-so putting in any of his money for this next round?"