ABS headliner question

I'm going to be installing a new ABS headliner in a few days (got it from stock interiors and it looks great), and never thought until now about insulation. The underside of the roof area has surface rust, so I planned on coating it with RustReformer, have used it before and been happy with the results. I'm wondering though what any of you guys have used for insulation above the headliner. I'm not interested in using DynoMat or anything like it. Do I need insulation at all? Let me know what you guys have done and if you are happy with it. Thanks.