For longer term storage, there are many self storage units around the metro area. Not cheap, but then neither is paying extra baggage fees and lugging around extra stuff not needed for another leg of your trip, as it sounds like Terry might be doing. For example, I found "Downtown Denver Self Storage" with units starting at $45 a month. http://www.downtowndenverstorage.com/
Steel thickness: lockers tend to be made from a standard thickness of steel, which is commonly 0.8 mm. thick; but heavy-duty or high-security lockers are offered as a standard option by some manufacturers, or may be available on special order. A typical locker of this sort may be constructed from steel 1.2 mm. thick, for example, and is usually fitted with three-point locking, regardless of the number of tiers.
Stored my luggage for several hours at Lugden. Great location just across the street from Union Station. Spoke with the owner and he said he owns the parking spot so they are always there during the day. Prices were reasonable and I felt comfortable storing my bags there while I explored Denver. The owner was nice and gave me coupons for some local businesses.