Safehouse Armory is an option for Safehouse Room A and Safehouse Room B. You can buy the receipts from Bits and Pieces in Solitude.
Requires Legacy Safehouse Plus.
Version 6 update: Legacy Safehouse Plus has been integrated into Legacy of the Dragonborn SSE and should NOT be installed as a standalone mod.
Armory Room A
If you buy the "Safehouse Armory Receipt (A)" (6840 Gold), it will be automatically added to the Household Planner in the Master Bedroom. Here you can set up the room to contain 6 mannequins and an extensive assortment of weapon racks, plaques and display cases.
Armory Room B
If you buy the "Safehouse Armory Receipt (B)" (6080 Gold), it will be automatically added to the Household Planner in the Master Bedroom. Here you can set up the room to contain 5 mannequins and an extensive assortment of weapon racks, plaques and display cases.