The present invention provides modular trays having cutout features that are configured to engage with a mounting feature of one or more removable rails. The removable rails may be removably secured to a tray body in a plurality of positions to allow a user to install or uninstall rails to support different sized fiber optic modules. For example, a tray may support a twenty-four optical fiber module, two twelve optical fiber modules, or three eight optical fiber modules. Fiber optic enclosures housing the trays can be affixed to the outside of a fiber optic enclosure and allow for easy stacking and unstacking.