Do not assume anything!!!When you are thinking about using somewhere as storage then SAVE. Put something inside the container (like 1 gold), travel elsewhere, wait perhaps 35 days, return to see what happened, then regardless of the outcome revert to the save. This takes about 20 minutes so if you cannot be bothered to do it you really do not deserve free containers...
One character I play is an outlaw and cannot rely on houses in towns. Hence I need bases out in the wilderness from where to hatch my nefarious plans.
Two examples;
1) This character married Gilfre thinking great, two free houses away from towns, except using the above method I determined only the chest, wardrobe and sack outside (Gilfre's House) were safe. Everything else resets, although items you drop (in the Worker's House) appear to remain there. Even though the sack outside indicates you are stealing from it I have not had a problem storing items there (beyond 30 days) and to my knowledge they are not being tagged as stolen.
2) Gilfre's house did not particularly suit this character, so I tried Anise's shack (after killing her when she attacks you for using her cellar). Again, using the above method I determined everything in the area was safe EXCEPT the barrel upstairs. Let me be clear about this!
You get TWELVE safe containers, an Alchemy Lab an Enchanting Lab, and a bed, for free, out in the middle of nowhere. Presumably you would only live somewhere this isolated if you were, uh, bad to the bone, so also note that you can jump onto the steeper rock ledges near this place and kite the thugs/assassins that inevitably come on account of your pilfering (useful at low levels). You can creep into Riverwood (at night) to use their forge, tanning rack, workbench and grindstone. A smelter is harder to get access to but there is apparently one outside a mine some ways to the west beyond the lake.
Obviously Skyrim being Skyrim, issues may yet occur with this place, so I will report back here in future if I find anything amiss. Long story short, CHECK containers before using them. Have fun with that shack but
CHECK IT AGAIN YOURSELF BEFORE USING IT. You never know, right?