I spray paint mine lad! Rustolium Mat Black does a good job, doesnt peel off as much as other paints!
I dig my sets similar to yourself, and use fish heads, as bait!
If your getting alot of rats, may mean mink are thin on the ground, ( might be someone else trapping the area)
You could always try feathers in the back of your sets instead of bait, to keep the rats out! A few in the back, and a few placed outside the set works well!
I don't have much trouble with people spotting my traps, because i finnish up this time of year! Saying that, i do usually put my sets in overgrow