I've never seen the benefit of any "padding" inside the baffle for speakers of the size we use. When you're building a huge enclosure for 12" speakers, then killing off any back end sound may make a difference, but I doubt you can tell with speakers the size used in O-scale model trains.
If you really want to see samples of well designed speaker baffles, check out laptop speakers. Those companies put some serious sound engineering into making tiny speakers sound really good!