I added casters to a Craftsman side box several years ago. Seems it was taller than the base unit of the combination I bought 40 years ago, so it wouldn't hang on it. Oops Figured casters were a better solution than just sitting it on the floor. Did it entirely differently, but bottom line, whatever works is the right way, at least for me. I may have used the wood spacer idea if I'd thought of it though...
When we built a garage a couple years ago, I figured a 72" Harbor Freight box (coupon, $200 off) in the cost. Laid an old, 36x80, solid door I picked up for free on top for a work bench. Yeah, it's high, which is perfect! Working on small stuff bent over just isn't fun with a couple of messed up body parts. Big stuff goes on the tractor lift.
For me, the Harbor Freight unit is a good box, for my Ford Technician brother, he'd wear out the drawers in a year with the repeated, every day, use. Mine sit there closed most of the time, especially in winter, so they'll last forever.
While this is a machinist forum, and I've been dreaming of delving into actual machining for 50 years, so far it hasn't really materialized. My boxes are filled mostly with hand tools, measuring equipment, files, some engine tools, stuff. Other equipment includes a stick welder, acytelene torches for heating and bending in the big vice (after I broke a medium size vice), various angle grinders, chop saw, a newly purchased 4x6 bandsaw (Love those coupons!) and lots of hammers for fine tuning.