Not that I'm being booked to fly anywhere for a wedding, but I have a question.
How do those of you that travel for your weddings calculate your expenses? Do you add 10-20%? And if you usually hire a 2nd gun to run a camera, how do you calculate that as well?
(If I usually pay a guy $300 to run another camera, do I still pay him $300 to travel 4 hours somewhere overnight?)

Just curious as to what the norm is.

We charge either a mileage fee (for driving destinations) or an airfare fee (for flying destinations), as well as a lodging fee. The lodging fee has a bit extra to help cover meal costs. As for assistants, they are paid for the hours they are working as well as the business hours that they are out-of-town.

So to answer your question, if you normally pay your assistant $300 to film a wedding with you, then I would pay him more if he has to be out of town for a day or two in addition to that. Otherwise you may find that it's not worth the hassle for them to go with you.

Although I don't travel for videography assignments, I do travel for computer consulting. When doing so, I have an hourly rate I charge while working with a minimum and maximum number of hours. Any expenses are passed through to the client. I always try to keep the expenses to a minimum, but try to stay close to the work site. Hope this helps.

Not that I'm being booked to fly anywhere for a wedding, but I have a question.
How do those of you that travel for your weddings calculate your expenses? Do you add 10-20%? And if you usually hire a 2nd gun to run a camera, how do you calculate that as well?
(If I usually pay a guy $300 to run another camera, do I still pay him $300 to travel 4 hours somewhere overnight?)

Just curious as to what the norm is.

Hit up the IRS for their Per Diem rates based on major metro areas, or out side of the US areas. That is a good food & lodging cost estimate. Then tack on air fair and and "down time" fees for time spent traveling but not shooting.