This telescope cover provides permanently mounted telescopes and telescopes in storage with a secondary layer of protection from the elements.  Even within an observatory there can be a lot of air movement with wind-driven dust, snow and rainy mist blowing through.  Scope Baggies are simply large industrial duty plastic bags that function as low cost telescope covers. 

In the semi-protected environment of an observatory the bottom of the baggie remains wide open to allow air circulation and inhibit condensation.   It’s time tested and works wonderfully well.

The Scope Baggie is absolutely not intended for outdoor use.   Do not even think about it.  Sun will overheat a bagged telescope and moisture will condense within the baggie.  Insulated reflective silver outdoor covers are several times more expensive, more bulky and require careful handling.  But if you need a cover for a scope being left outside spend the extra money and get yourself an outdoor cover.