According to this Respawn and DeadBody Timers mod on SkyrimNexus:
Vanilla Respawn Timer details
Npcs, Creatures and Items... respawn after 10 Days or 240 Hours..
Areas that are marked cleared on your map respawn after 30 days or 720 hours
Merchants Respawn Items every 24 hours..No Change..
Dead Bodies Remove themselves after X amount of Day
and If More than 15 Dead Bodies are in cell then Remover Features kick in
So, no. It is not safe to store anything in corpses.
I've read that named NPCs do not respawn in Skyrim. So Alvor won't come back (ie. it won't be reset). I wouldn't bet on his corpse staying there forever though.