D.W.
Cloth at night would save you from buying diapers ;) I use cloth at night almost exclusively. I like the thirsties fab fitted with a couple of hemp liners. Trainers aren't going to help at night. You'll just end up with a bigger mess because they aren't designed to hold as much as a diaper. I never equated diapers with being a baby so my son never had problems using a diaper at night for bed protection, as we called it, even when he was 4 and fully day trained.
You absolutely can not work on night training. It's a matter of when their body is ready and for the vast majority of kids that is around age 5 and up to 6 is normal. It's a physical and neurological development. The body has to be able to either hold the urine all night or wake up to go and there is no way to make that go faster.