I made some home-made insulating paint for the floorboards of my 57 Chevy. Works great for heat and noise insulation.
I was looking at Lizardskin, but thats $80 a gallon and then you have to buy their sprayer. Then I found "glass microballoons" at an aircraft supply house and mixed them with a gallon of "oops" paint (the ones at Lowes where they mix the wrong color) I used outdoor latex, mixed in the micro balloons and painted it on. Its an ugly texture, but I covered it in carpet, so it did not matter.
I did one side of the floorboards and left the other side alone. then put two of the same wattage bulbs underneath the floorboards and after a while the untreated side was much hotter than the treated side. Not that it matters for a UDS, but the untreated side sounded kinda "tinny" when I knocked on it but the treated side had a "thud" sound. Heat and sound protection, and it was pretty cheap.
I bought 2 gallons of the glass micro balloons, mixed up two gallons of paint, and I still have more than a gallon of the microspheres left. They go a long way. There are pretty cool too, because they are obviously a solid, but they flow like water.
ps: you have to be careful mixing them. If you use a power mixer you crack the spheres and that ruins their insulating properties.