You sound like a loving mom who is cares very much about the lives of her children and I commend you for that. These are never simple situations, but here is my read on your situation:
It sounds like you have more than one problem.
1) You have what you believe to be legitimate concerns about your daughter. You would like for her a better scenario than what this man will offer, and you don't believe he will make her a priority, and I get that. But I think the best thing you can do is pray for your daughter and this relationship, pray for this man, and pray for God's wisdom for yourself and them. I actually think you could have far greater influence on your daughter as long as she lives with you, by loving her, praying for her, and showing her unconditional love and allowing God to work through your relationship with her and the example you set for her. If this is really as simple as you not approving of the choice of man she is interested in (and not her behavior in your house) I think this is one of those horrible things that parents have to go through while they allow their adult children to make decisions that they feel are wrong.
2. Also, it appears your husband has already decided how he wants to handle it. I personally think the worst thing you could do is to openly fight against her father (or your husband) because you disagree with him or to quietly subvert his leadership. Perhaps this is a great opportunity provide your adult daughter an example of what Christ calls for us to do as wives. If your husband is against providing resistance to your daughter, I would also spend more time trying to understand why he feels this way, as well. I honestly believe God can do more through you as an example of a Christian wife, your relationship with your daughter, and prayer.
Ultimately, if it is your goal to prevent her from choosing him, I believe that no amount of your attempting to convince/coerce/punitively effect her decision to pursue a relationship with him is going to work out for either of you. Are you prepared to have your relationship with her destroyed if she chooses to continue this relationship? This is only going to backfire on you, and perhaps (as your husband said) push her faster/farther into his arms. Instead, I would draw her close and love her and spend time with her, try to learn why she is interested in him, and allow her to seek your advice rather than you attempting to convince her and force her to do what you believe is right.
Most importantly, pray for her. You can't prevent your daughter from making bad choices.
Finally, did I already mention prayer? We simply cannot underestimate the power of prayer, and how God can work through us when we don't get in His way.
p.s. My mother went to great efforts to force my grown sister (23) not to move and marry her current husband. She's happily married and has 3 kids now with this man, and he's been a good husband to her. I'm not saying the situation is identical, but it destroyed their relationship for a couple years, and it still isn't "good". Oh, and because she made it unbearable to live at home, she ended up moving away much earlier than she probably would have, had my mom not issued ultimatums and the like. I'm not saying it's the same situation, but it all came from my mom believing that my sister should be with a "better man".
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