56 3100 Cab Insulation

Has anyone ever tried/heard of insulating the pillars, doors, etc with like a spray insulation? Or are there alternate ways to effectively minimize road noise?  

The same folks that make Dynamat also make a product called Dynashield, its a spray on coating that serves as a sound deadener. Eastwood offers a similar product, and both have rattle can or spray gun packaging. Any "rubberized undercoating" will do about the same, but some probably adhere better than others. Of course stick-on sound deadening mat is pretty hard to beat, especially if you use plenty. But its high.

Beyond that, theres a product available at home improvement stores called Great Stuff. Its a spray can with wand that shoots expanding foam into voids and cracks. That would be good for filling A-pillars and possibly other cavities to stop drafts, provided that it never gets wet because it may retain moisture. Another idea is to stuff any voids behind like cab corner trim panels and kick panels with some good ole fiberglass house insulation just like you might in a woofer box.

Weather liners behind door panels are always good too. Undercoating, grommets for everything, good seam sealer and glass weatherstrips, thick floor mats, good carpet insulation, etc. Theres a lot that can be done, but the old trucks were built pretty loose, bodywise. So things not fitting right can be an issue, too.