DD Went through a stage like that too at a similar age too I think we used to put a nappy cover over her when she went to bed (and wasnt in view) or we would check her and she would have a bare butt!
I have to agree that showing him a potty cant hurt, cause I dont think your DS is too little. If he doesnt like it or isnt interested then you know that the nappy removal wasnt related to that DD started on the potty at 11 months and was not in nappies of a day at 18 months with very few accidents, now we just have to get knickers back on her!