A model of a thermal print head is provided that models the thermal response of thermal print head elements to the provision of energy to the print head elements over time. The article may have a total porosity of at least about fifty-five percent, above sixty percent, or even above sixty-five percent. Thereafter, the sealed package is placed in an environment substantially free of the test gas and allowing the test gas to diffuse out of the internal space. Here, when in the deployed position, abutment of the portion of the vehicle’s door with the deployable step, prevents the deployable step from moving towards the stowed position. The cart may further include a detachable bridle support that is receivable on one of the conveying member, the storage member and the independent support.