Improvements in a linear guide self-tracking modular telescoping structure is disclosed. The cover can be sized and fabricated to provide protection to a number of different uses from covering vehicles to offices, storage and operating rooms. The structure provides a fairly rigid shell to protect from objects falling on the cover and also to protect from snow loads. It uses a telescoping enclosure that retracts to occupy a small footprint when retracted. It may also include a side access door to allow a person to access the side of the structure. A power mechanism can extend and retract the cover as it is guided by the self-tracking rails. Seals not only protect from wind, snow, sand storm, extreme temperature or weather and rain, but also from rodents and insects that can accumulate within the structure if it is left unattended for a period of time.