The single best way to ask to join a trusted list for a profile is to use one of the links on that profile that says "request to join the Trusted List" -- either the link on the right-hand side of the profile or the one under the Privacy tab. As the link on the Privacy tab explains, after you fill out the request form (including a note explaining why you are making the request), an e-mail will be sent to the Profile Manager(s) and you will be informed if you are approved.
Not only is this just a single step for you, but approving requires just one click from the profile manager. That's a good thing, since some members have difficulty figuring out how to enter another member's email on the Privacy page in order to give them Trusted List access.
One caveat: When you make a Trusted List request, you don't get a copy of the form you sent, so you might want to save your text somewhere for future use.
And note that the "Requests" item under the My WikiTree tab will show you a list of your recent Trusted List requests and their status.