I think you can appreciate that some may exhibit skepticism; especially since all you list for credentials is a movie data base link. I understand why you would want to have an email for the separate projects you are working on.
As a suggestion, to legitimize yourself a bit more, how about doing a YouTube explaining what you mean; show your face and surroundings. What about a business card or a phone number? I am not sure how free lancers work or what the business criteria are. Do you have established references? Other projects you worked that can be checked?
And, in order to work as a producer (freelance or not) in Hollywood or Los Angeles area, do you need or have a SAG card? Or is that for actors only? You must have other credentials you can provide to people who may be interested in a project such as yours. While the idea may be attractive to some people, your answers are a bit vague.
I would think there would be a contract involved laying out what is covered in expenses, fine print and what expenses would not be to protect both parties. And what about medical expenses, insurances? And when you write, "the right candidate" - what if someone who is a bit disabled, never traveled but would like to now, would you consider them? There are a lot of factors involved.
The all expense paid, trip of a lifetime, human interest project you're offering would mean that you would follow the person around from morning to night? What are the boundaries? How many in your film crew? Besides your involvement, are there investors helping to pay or is the travel service funding it? Who is the travel service you are doing this film for? Where are they located?
I am not saying you are not sincere, but you do need to lay out a more-detailed plan so maybe those interested, would be more comfortable contacting you.
If you contacted the Rick Steves' corporate office, and they support the idea of your invitation to people, then maybe prospective travelers would feel a bit more comfortable.