How much polyurea do you get with the cartridge spray product, and what is the coverage?

Each case of 6 cartridges is sufficient to cover a full size pickup over the rails. Smaller beds (or under the rail applications) can be covered with 4 or 5 cartridges to sufficient thickness.
Total gallons per case of 6 is just under 2.4 gallons.
There is no loss of volume by evaporation, so what you apply is what you end up with.