The writers have become sloppy. There's no mention of how or if Dexter cleaned up the trailer after the kill. This guy is about to sue the city, is a major suspect in an ongoing case (just because the confession is thrown out doesn't mean the case or investigation is over), and Deb is obsessed with getting him. If he suddenly disappears, and his trailer is left there... the police are going to look at it and one would think they'd notice there was a fight in it. Even if Dexter got rid of it "off camera", is obsessive Deb just going to pretend like she doesn't care anymore? This is Deb we're talking about.
Then there's the straps in the crematorium, as well as the ashes of the guy. These things just don't vanish... and metal doesn't disappear when someone is cremated.
I'm being picky, yes. But being careful was Dexter's "thing", the writers made a point of highlighting this during every kill. Now that stuff is forgotten about because he has to have a heart-to-heart with Deb.
This show has gone from a good (never great) show, to almost a guilty pleasure.