The portable restroom transport trailer from Johnny Mover Trailer Sales has a skid-locking system using an iron bar with a chain-binding system to secure multiple units. Models are available to handle six to 20 restrooms, and all feature brakes, paint options, lighting, leaf-spring suspension, front deflectors to protect units from road spray and debris, and optional powder coating and chrome wheels. 800-498-3000; www.cesspoolcleaners.com.