Depends on your ambient humidity and the types of filament you use. I wouldn't say it's absolutely necessary - I've had cardboard spools sitting in cardboard boxes for years that still print just fine. But when you're going to print something...
Requirements:
Store 6x 1kg spools in an environmentally protected 500mm x 250mm area
Dehumidifer / Silica Gel
Cheap
Able to pop open a lid and grab a spool without removing other spools
Problem: It doesn't exist. (Although a plain ol'...