Again, more detailed information is in order. I've seen special camera boxes mounted (and have used them myself), and I've seen camcorders duct taped to struts. I've done a lot of flying with doors off of single engine Cessnas ranging from 182's to Caravans with photographers in and out of the aircraft, as well as hanging from the strut.
I've attached various items to aircraft struts using a variety of means.
What exactly is it that you're trying to accomplish, using what equipment? How large? How well faired? Weight? Position? Intended means of attachment? Type of aircraft? Type of operation? Door on or off? What kind of budget? You needn't reveal confidential information, of course, but any information is a plus.
Details are useful. Your best bet, as always, will be to sit down with a designated engineering or airworthiness representative, and get an approval written up.