how to place (boss) mobs with custom inventory in worldgen structures [1.20.1]

I am trying to replace pillager outposts with a post apocalyptic structure that has pillagers with different guns waiting to shoot at you.
I have a custom summon command that sets their movement speed to 0 (so they stay on the guard towers and shoot instead of jumping down), equips them with all the items and makes them persistent.
I know it is possible to use spawners/mods/etc to make random spawns in structures or to modify the default mob equipment somehow but that doesnt really solve my issue.
I want to place them in a few specific locations (look at example image)
How can i place pillagers with custom inventory at predetermined locations in a structure.
When i save them in the structure their inventory is lost.