Truck Bed Liner Spraying?

Most of the bed liners spray on with a Schutz gun. They're a special, heavy spray, applicator. See here for an example.
http://www.autobodytoolmart.com/3m-schutz-applicator-gun-08997-p-11269.aspx

A lot of bedliner coomes in kits that include a Schutz style gun. Several places sell an inexpensive model.