The cabinets in the trailer were tall and not well separated, so there was tons of wasted space.  I just took some 1/8" ply and painted it and drill holes in the four corners, printed these out, and viola, instant shelves for the cabinets.

I did 1", 2", and 3", and I use one of the 1" to cap off the top shelf so it stays solid.

I used PLA which actually might be a mistake in this case.  The trailer gets pretty hot in the summer and they started to bend a little and warp.  I would suggest doing PETG.  It also seems (I could be wrong on this) that PETG has some natural lubricity to make screwing them together easier.  PLA seems to be very sticky in that regard.

Message me for the fusion 360 file.