In terms of recommendations, hmmmmm, I'm having some of the same issues myself.
First, if they're well-fed and they're not hungry, then they don't have much incentive to come eat. There are about 5-10 people putting food out in my area and the remaining cats look at my traps with a shoulder shrug, like, "Yeah? OK funny guy, we've seen you here before and there's 5lbs. of food on the old lady's porch." I think if the food gets cut for a day they'll have more incentive.
One thing I've been doing is making a tuna fish oil/water mixture (make sure there's no sediment) and keeping it in a large spray bottle in the fridge. I make sure it's really smelly. We had a feral go MIA last week and I sprayed down his usual area with the fish water, and when I came back an hour later he was sitting there. So I guess that works to get their curiosity up.
Obviously, feeding them in the same place regularly works. We have a neighbor with a crate on her balcony, and the cats come to the balcony to eat. She's moved the food into the crate to get them used to it. I'm not sure if they've gone in, but they're definitely more comfortable with a crate or trap on her balcony than they are seeing me walk a half-block with a big crate in my hands, plunking it down in front of them. Unfortunately, living in a big complex, I can't just leave traps out and come back later.
So far, tuna has been irresistable to them, and they only get comfortable if I'm sitting far away. They might not come into the cage for the tuna, but if I toss a bit in front of their nose they're definitely on top of it.
So I suppose some tuna, some scent marking, some work on getting them used to the trap or cage, regular feedings, and denying them food for the day before trapping will help get them going.