I have an aluminium DJ transport box for mine.
It holds about 300 singles in 3 vertical rows of 100, and the top and bottom of the box are about the same height so when you lift off the top it's easy to flick through the singles.
I keep each single in it's paper sleeve with a polythene cover over that. The poly bags only cost a few pence each and they prevent dust andsave the paper covers from being ripped.
Locked up it's about the size of a suitcase and very handy to stow away.
Thorens TD521, SME3012, DV-20X, Creek OBH 18, Cambridge Audio A5, Cambridge Audio P500, Castle Chester, Creek OBH 21SE, AKG K702