I haven't got a fretless (though it's on my list of "to gets" & a fretless 5 is at the top), but I hate that traditional 80s chorused fretless.
Saying that, there's nowt wrong with some reverb & if the chorus is done right, then yeah.
Maybe a delay & a filter would be good choices. But it depends what you're after.
Mine's would go through octave, fuzz, filter, LPF & chorus & sound more like a synth.