With such a high degree of sentimental and/or personal value, I would recommend displaying the model and diorama in a enclosed glass shelf to avoid dust or dirt accumulation over time. To clean, a microfiber or cotton tipped swab could come in handy to wipe large surface areas. If you mold the cotton tip, it could potentially clean those crevices at perpendicular angles. Beautiful mini display you have there. I predict many more models in tow in the near future