Storage owner has a tenant who hasnt paid the rental fees for a year....sends him the required notice which comes back unclaimed....owner calls tenant and tenant say he has no money.
Storage owner removes tenants lock and replaces it with his own....storage area is full of tenants property....
Tenant cuts the lock the owner put on, and removes all of the items in the storage building.....
Crim mischief? Burglary?
theft?
or purely civil?

If there was never a court order or other legal means to forfeit the owner's stuff to the storage facility owner for nonpayment, I have a hard time getting to burglary (what felony or theft was committed at the storage unit if the stuff was owned by the tenant?).

What I am wrestling with - as I am sure you are - is whether renting a storage unit is receiving a "service" akin to a hotel room, or if it is a lease of "property" akin to renting an apartment. If it can fall under the definition of service, I would say this is criminal under 32.04. If it is a breach of a contract with regard to a property right only, it would be like seeking an eviction or suing for past-due rent and would be more civil in nature (unless, of course, there was fraud in the initial application - which raises other issues entirely).

What does the contract say?

I vote civil. Landlord's remedy is (was) to foreclose his self-service storage facility lien per Property Code Ch. 59.

http://www.statutes.legis.state.tx.us/DocViewer.aspx?K2DocKey=odbc%3a%2f%2fSOTW%2fASUPUBLIC.dbo.vwSOTW%2fPR%2fS%2fPR.59%40SOTW&QueryText=storage&HighlightType=1

I had this exact situation come up a few months back in my county. I couldn't find anything beyond a Class C Criminal Mischief for the value of the lock.

With no research whatsoever - Hindering Secured Creditor?

i have had all those same thoughts.....seems very borderline to me....as an aside.....no one know the value of the property removed.....the amount owed on the rental at the time of lockout was 1500.00
i have not had time to look at the elements of a secured creditor yet....

If I am not mistaken the key to this will be the terms of the written contract if one exists. If a written contract exists and it provides for a possessory lien to secure the tenant's breach, this I believe would be called a warehouseman's lien and is treated similar to a mechanic's lien where a mechanic works on a car, refuses to release it until he is paid, and the owner takes it without permission and without paying. If no written contract exists then the class C criminal mischief is about it. Naturally the owner of the storage units has a civil remedy.