Next month I have an opportunity to shoot in Mexico City for the company for which I work. I have shot in Canada and that is no problem. I drive across the border from home base near Seattle. Don't do anything...tell the folks at the border that I am meeting with the Vancouver branch of our business...which is true.
But for Mexico,we are flying of course. I won't be taking a full kit...mainly just camera and sticks. The gear is not worth a huge amount, but it would be not good to lose it. (the gear is mine not the company's.)Sachtler tripod and long in the tooth Sony sd camera.
I have researched a bit...and some say just go across...don't mess with carnet etc. However, I will have a tripod...so I think I will appear to be other than a tourist.
Just declare you are carrying professional equipment on your customs form- with no monetary value. If it's bulky- you'll be asked to register so that they can confirm it leaves and isn't sold in Mexico. But you won't have have to pay any duties as you have the right to bring in a non-professional looking camera as long as you leave with it. Carnet etc is not needed for the amount of stuff you're bringing. Insurance- get gear insurance to cover Mexico if you're concerned.
BTW- if you need any production assistance or rental gear- contact my wife's production company Simplemente. They're based in Mexico City and can help you out bigtime. :)
Basically what Noah said. If you are identifying yourself as part of a company, on a company-related job there's just a form to fill out and you SHOULD be good to go.
What you DO need to be aware of is whether or not your insurance covers your gear OUTSIDE the US. Most, I believe, does not. Check with your insurance agent and add this coverage as necessary.
My main concern shooting in -- a border town of -- Mexico was security. Luckily the client was willing and able to provide transportation and a couple of guys who I was glad were on my side and not vice versa.
I too am shooting in Mexico next month and would rather rent lenses and my d5 mk3 down there rather than carry back and forth. I contacted Simplemente but they have not responded. Do you have a personal contact there?