As a beginner, you are not alone in thinking of bonsai as "delicate" and "sensitive." They are nothing of the sort, particularly junipers. Junipers are among the toughest trees out there, inhabiting some pretty desolate, stark places on the planet.
The reason they get root rot as bonsai has everything to do with owners not understanding dirt. In the wild, junipers are native to soils that drain well. The earth has almost unlimited drainage, since water can flow out of the soil quickly to another place. In a bonsai pot, that's not the case. Soil that holds too much water doesn't drain. The water stays in the pot and suffocates the roots. This is especially true if you're using soil with organic (bark, etc.) components. Plain old potting soil sold at nurseries is MEANT to hold onto water because mostly it's used for indoor houseplants.
Good bonsai soil is made up of irregular, larger particles that don't break down. The components used are meant to drain well, but retain water inside the particle, giving it up over time.
Rain is not a problem with bonsai planted in the right soil. It just flows through for the most part.
Don't baby your trees and treat them like hothouse orchids. They are not. They actually REQUIRE wind, rain and weather to stay healthy, just like trees in the wild.
You haven't specified the area where you live--state would do. Local climate is critical to what kind of care you need to give.