Ditto on what they both said above. It's generally renters policies that are consistent with the 10% rule.
On the standard HO3/HO5 it's 10% of coverage c. For contents in storage. I don't know of any carrier that will cover a specified amount over 10% without endorsement. You're looking for HO 06 14 increased amount for personal property in a self storage facility. Not every carrier offers this endorsement
It's 10% not $10K
Some carriers extend the full contents limit to storage units but some limit to 10%. Double check with carrier because a separate residence limit may not apply to storage units since they are not a residence.
Travelers offers 100% contents away from home.
Usually they have 100% of coverage c as long as it isn't a residence other than the residence premises. Storage units aren't a residence so the 10% restriction doesn't usually apply