Letting loot spawn in custom placed objects, is much much much easier!!!
Just run a little script within your init.c and startup your server with it, and in between 1 or 2 minutes it creates a new mapgrouppos.xml
Replace that new mapgrouppos.xml with the older one (you will notice that the new mapgrouppos.xml file is bigger).
Check the link below on how to!
https://github.com/Arkensor/DayZCommunityOfflineMode/wiki/Enable-loot-for-custom-placed-objects
Cheers,
Mr. Groove