I am wanting to order your kit, and wondering what size bezel I need? I ordered MTX Terminator6S speakers from Crutchfield and they say that 4.875 is the I.D.? Does this jive with you?Promaster is a fairly easy audio upgrade.
We offer a kit which includes 3 linear ft of Thinsulate(TM) (enough for both cab doors) and our CNC machined PVC (not mdf) adapter rings (with proper bevel) for a variety of after-market speaker cut-out diameters. We offer these to Transit and Sprinter folks so didn't want the ProMaster crew to feel left out. Our adapters (as you can see below) provide a much more secure mounting than a flimsy plastic ring. We also back our adapters with VHB tape for a secure rattle free connection to the door structure. Great way to improve audio quality and also reduce road noise with a bit of thermal benefit also.
A good place to compare speakers is on Crutchfield. Then shop on price at the other online stores. Or go to your local Car Stereo Shop. If retaining the stock head unit, look for speakers with more efficiency and lower watt ratings. Many of the higher end speakers will demand more power than the factory audio system can deliver. One way to offset this is to add a powered sub like the Alpine PWE-S8. The amp in the sub will drive the bass tones which then reduces the need for the door speakers and head unit to create the power hungry lower audio frequencies.