The following tool is not an original idea, but I think it is worthwhile mentioning. Someone I know spent a lot of time building a resin box car (and did a nice job of it) but in a moment of inattention laid it down and crushed the delicate stirrups.
I like to use a simple handle, made from a 1/4″ wide brass strip with a hole at each end, for painting car models.
It simply attaches where the truck screw holes are…
…it keeps fingers well away from airbrush spray….
…and it prevents one from laying the model down on the delicate underbody details. Of course, we still need to be careful of the other fine details, but I find that I usually lay the model roof-down on my soft-foam cradle. I do have to be conscious if there is a vertical brake staff.