Many months ago, I won a dozen K-Line aluminum tankers from Cabin Fever, a haul I nicknamed "Tankerpalooza" for its entry in this thread. Those tankers had been sitting on the back of the couch in my living room ever since receiving the shipment on 11/22/22 (yeah, it's been that long 
) because I didn't have any boxes that fit them. The BCW card boxes I employed for many box-less cars didn't fit those cars owing to their height, and I got wrapped up in a project to slice up surplus styrofoam coolers to approximate the foam end cradles of the original K-Line boxes (I had not gotten around to attempt the same with the outer cardboard window box) .
Well, since then I found that the smallest of the K-Line aluminum tankers do indeed fit the card boxes. Barely. The larger 50' tankers do not, however owing to their larger-diameter tanks making them too tall to fit. Fast forward to 5/22, when @coach joe pointed me to BCW's two-piece "vault box". As I was perusing the listings on BCW's Amazon store, I noticed another new addition to their lineup, called the "Quick Fold" box. This looked like an ideal solution -- uncover a quartet of adhesive triangles, pull the ends and the box assembles itself. it even has a lid with a magnetic fastener. There's just one caveat... at 3.25" wide and 4.19" tall, they'd fit the tankers...wheels down. While that would technically do the job, the idea of having to extract the cars in that orientation led me to tour the suggested alternatives which led me to a generic variant that permits the cars to sit sideways relative to the lid:
The card box as it comes from Amazon, with the listing superimposed if you want to look them up. The white triangles cover pressure-sensitive adhesive that gets pressed against the extended corners of the flat box when you pull up the box ends under which the instructions are tucked.
...Remove the triangles, pull the box ends and press the adhesive against the corners. That's all that's needed to assemble them. The magnetic catches snap shut when the cover is closed. Can you play Samsonite gorilla with these? No. But they'll keep the car inside under normal conditions, and if you want stronger magnets, you could always glue additional flat rare-earth magnets on the lid (the actual magnets are on the box, the lid just contains metal discs)
The toploader box on the left, a standard BCW on the right. I bought a bunch of the latter in 3 sizes to finally box up a large chunk of box-less auction wins. At least they'll be stackable now. The MTH 50' boxcar and coke hopper will need some other solution since the magnetic-lid boxes only appear to come in a 13-ish inch length.
These boxes internally measure 3.25" wide by 4.25" tall. Here's the K-Line 50' aluminum tanker. While the 13.2" length doesn't quite accommodate the couplers on these cars, they'll fit if you turn the trucks against their stirrups.
The RailKing woodside caboose? Fits, even with that firecracker antenna atop the cupola
Premier N6 caboose? Fits
RailKing or Premier extended-vision cabooses? Fits and Fits.
Now, you may notice the excess room on either end of these cars. That might (will) lead to a lot of unintentional back-and forth motion. These aren't boxes for shipping, these are boxes for neatly stacking rolling stock on a shelf boxes. That unintentional sliding/rolling about while moving them around though....
The card-box vendors have thought of this...at least for trading cards. A number of vendors offer pre-cut foam blocks intended to fill space in your card collections, and these work equally well at keeping your rolling stock put. Above is how they arrive from Amazon...at least from this unnamed vendor -- others might pack theirs differently. This one packs theirs in a vacuum bag. There are 40 foam blocks compressed inside this package 
Slice open the bag, and they quickly expand to full size. I have yet to fill all these boxes with my winnings, I'm designing post-it labels with all relevant info (including photos manufacturer logos, catalog numbers and maybe even UPC numbers) to stick on the box ends.
Now, there is one rather sizable elephant in the room -- These aren't cheap. The BCW quick folds come in a three-pack for a little more ($24) than what these cost, but either way they're still spendy compared to the standard white cardboard boxes. I only acquired enough of these to house the large K-Line tankers, and maybe a few more for the MTH cabooses needing the headroom. It's still a pretty bit of change, which may or may not be worth it depending on their usefulness and your budget.
---PCJ
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