I am talking as the woman here since most answers are from men.
If your wife feels comfortable doing this then don't insult her by telling her you "won't let her". I am going to assume your wife is intelligent enough to make the decision not to go if the weather is bad. If it starts to get bad then I would think she would turn around and come home.
As far as the inspection goes, if she feels comfortable enough she can inspect what you both are buying then why can't she?
If there are issues on the way home towing, a breakdown or whatever, can your wife call for assistance?
As far as having company along for the ride maybe you both have a friend male or female that can go with her.
Now don't get me wrong here I am not pushing the women's liberation movement here, if you knew me I am not that person. However, from posts I have read it sounds to me like a lot of men either do not think that your wife is capable or she shouldn't have that responsibility. I also am reading that many men are genuinely concerned about the safety of a loved one . I totally agree, we would all think that way.
This decision should be your wife and yours decision. Don't be influenced one way or the other by opinions that do not know you and your wife. If the weather is bad, the trailer will wait. Enjoy it when it does arrive.