Having sadly failed to build a (good) working pump trolley after four designs, I thought I should try bringing one of my other previous ideas to reality instead. When I showed an opening smokebox door mod I found for a TrackMaster Thomas, I added that seeing it inspired me to (potentially) build my own steam locos with them - albeit with real hinges in the right spots and an un/locking ability. With that, I made a cardboard test smokebox to see how I could actually do it. The plastic tube bits were used following Nigels' tip, though I'm not sure if I'll use them in subsequent designs.
Like the axleboxes on Rocket's tender, the hinges were made from (very) small bolts of staples. Even the idea to use a screw for a handle works how I thought it would, which got me fairly excited. I couldn't really seem to find good images of an American smokebox on the inside, so European ones will surely be easier to replicate. Like with cab interiors, I might initially use prints with or without details glued over before making them how they should be made. Given the scale is a bit bigger, I don't think I'll add this to a full locomotive in the foreseeable future.