Frame assemblies (10) for displaying sheets of advertising on portable structures such as portable toilets are adapted for durability and ease of use and maintenance. In various embodiments a frame assembly according to the invention may comprise a cover (32) for protecting sheets of advertising, a backing (34) for supporting the sheets, and various types of novel frame members (12). In other embodiments frame assemblies according to the invention can comprise sets (72, 74) of mating frame members (12), the frame members held together, when advertising is installed, at least partly by the interaction of flanges or other portions of the mating members.