Play Train Table Trundle

About as simple as a rolling storage box gets: a shallow 1x4 frame, a plywood bottom, and four small casters. The only real decision is sizing — this cut list is built around one specific train mat's dimensions, so measure whatever mat or play surface you're actually storing before cutting, rather than trusting the numbers verbatim.

There's nothing here that needs to be strong in the structural sense; the box only ever has to support a folded mat and some track pieces, not weight-bearing loads. Spend your care on getting the casters mounted flat and square instead, since a tray that doesn't roll straight is the one thing that'll actually annoy someone sliding it in and out from under a bed every day.