Shipping containers are the rectangular metal boxes that are transported on truck beds and loaded onto ships. They're usually 20 or 40 feet long, 8 feet wide, and about 8 feet high. Some are refrigerated and can be adapted for air-conditioned shelter. Shipping containers are easy to find and are generally inexpensive. One container is large enough for a temporary bunker to provide protection from extreme weather. Multiple containers can be stacked, set end to end or placed perpendicular to each other for more space and longer occupancy times.
Check your local building regulations before you begin, in case there are special requirements for your locality. Then excavate a hole that is at least 10 feet deep and the length and width of your container. Level the bottom of the hole. Use a crane to set the container in the hole.
Cut a hatch in the roof of the bunker to use as an entry. Hinge the part of the container you removed and attach it to the roof to use as a door. Attach a gasket around the door to cover sharp edges and create a waterproof seal. Use a ladder or spiral staircase to descend inside.
Provide ventilation for the container by cutting holes in the roof and fitting them with pipes that will extend above ground level. If you have concerns that your bunker will be discovered, plant bushes around the vent pipes or use other natural camouflage.
Cover the container with dirt and fill in any open areas on the sides. If the hatch is below the level of the dirt, either slope the earth gently away from it or construct a barricade around the hatch.
Create a catch basin next to the bunker by digging a pond and running a pipe below ground from the basin to the shelter. Attach a valve to the end that's inside the bunker so that the water can be controlled. Or simply use rain barrels to capture water and then pipe it into the bunker.
Use wind power to generate electricity. Install a windmill and attach it to batteries. Use the energy in the batteries to power small appliances or ventilation fans.