Just soundproofing before fittin roofliner.

Stuff at autobarn like dynamat is pretty exy, but on ebay one seller has epdm rubber soundproofing for auto applications with sticky backing.

has anyone used epdm rubber? wikipedia gave it a good rap for overall vibration absorption. but do i have to cover the entire surface in the stuff? Or can i just cover a fraction of the surface just like dynamat?

does anyone have any other more affordable solutions? spray on sound deadener was an idea, but it doesn't feel right. is it less effective?

At the moment the cannon exhaust is just screaming and will eventually be annoying inside (at the moment its friggen awesome ), and with no a/c, i want it to be insulated as best as possible.

thanks,
Chris.

With soundproofing it is all about mass. If the EPDM rubber has a reasonable amount of weight to i and is firmly attached to the roof metal , then it will do a reasonable job of dampening the noise.
Spray-on materials are typically too light to be very effective.
In my work we often do acoustic work for plant rooms. Typically we try to treat 80% of the surface area, so we pick the easiest 80%.

Cheers