I thought you wanted a cheaper solution.
yeah, you can spray coat with rubber, but not so sure how effective that is. I have heard it works. As rubber is a sound barrier, and its effectiveness depends on its thickness.
Jumbolon alone will not solve any sound insulation issues. You have to have vibration damping first. Without that, there is hardly any point putting in any kind of sound insulation.
BTW, a major source of road noise is your car tyres... just change those first to quieter tyres and you might get away with just the rubber spray on the arches and floor. Best bet are Bridgestone Turanza and Yokohama DB series, if you get the originals that is.