As you've worded your post, there's no reason why your ex-wife should have to tell you that she's selling the mobile home. Obviously, she has to abide by the agreement which she's entered into but (as you've explained it) that agreement only states what she must do after she's sold the mobile home. She'd be in breach of the agreement if she hung on to the money but, until the sale has gone through, your agreement doesn't give you any rights.
The fact that you didn't use a solicitor can't invalidate your agreement but, if you'd gone to a solicitor, he/she would have probably suggested inserting an additional condition, requiring your ex-wife to notify you if she put the mobile home up for sale. Without such a condition, you'll have to wait until the sale goes through and (unless you can find proof that she's completed the sale) trust that your ex-wife will notify you when the sale has been completed.
Chris