Yep, body traps, aka conibears, are for mink, beaver, usually waterway sets or paths leading to waterways. I have also set them on top of problem woodchuck dens.
I could tell you how to catch the fox in a leghold, but, you need to make sure no domestic animals would get caught. If there are any dogs or cats around, I guarantee they would be caught first. For something as large as a fox, you also need a large enough trap to hold him, or he will become trap wary. Are there any markings on the traps? For fox, I would boil new traps, then dip them in beeswax, then hang them out in the woods for at least 6 months to loose any trace of human scent. Then to set them, I would wear large rubber gloves set in the stream for a couple weeks. Now maybe this fox is not that wary, but the longer that trap is set without catching him, the better chance you have of catching a dog or cat, or a skunk, or a 'coon. Fox are indeed a difficult animal to trap.
You don't bait the actual trap. To make a "set", you would place the bait in an area with one way in and set the trap in the path. If you would like some good reading on this, pick up an issue of Fur-Fish-and Game at a good magazine shop. This is my favorite, most practical outdoors magazine. Furs have been going up. Up high enough I may get a coon dog and dig out my old traps. I can remember getting upwards of $70 for a coon pelt 25 years ago. They're up to about $40 now. I just got a gallon of chicken guts from a local farm. I'm going to put them in a glass gallon jar and bury them until late October and use them for bait. Yummy.
I think your best bet is a predator call early in the morning. You can buy tapes of them and play them thru a portable tape player, or a boom box. There are ads for these tapes in the magazine above.
Good luck, Andy.
For the record, there is nothing more I hate than to see an animal suffer. I used to use legholds out in the open when I was younger. Now, the only legholds I would use would be drowning sets. All others would be conibears which when set properly, snap the animals neck and at worst suffocates them. I believe in quick, clean kills.