Steve THX's box looked like heavy hardwood and was basically cylindrical which helped it resist resonance enormously. A box like your chest is going to shake itself to bits without some help.
Pine is very light and resonant, poor at damping vibration, it actually promotes it, is almost impossible to seal, shrinks and expands with humidity etc. etc. Making it airtight is more difficult than making it watertight. So how watertight can you make it?
If I absolutely had to use the pine chest: I'd build a thick walled MDF sub box to go inside the chest with room to spare and 'float' this 'real' sub box in sound deadening material. Using thick car body felt or carpet underfelt as a spacer. With the bottom of the pine chest almost completely cut away.
I often feel that problems with the appearance of a sub or speakers are entirely down to how one feels about items in room.
Nobody questions conventional furniture in a room. (Like a pine chest?)
Putting a pot plant or table lamp on a box sub. Even throwing a cloth over it to make it look like a small table. Works wonders if WAF rears it's ugly head. You can always lift the object off temporarily when you use the sub at high level if the object rattles or tries to hurl itself off.
I threw a dark green velvet cloth over each of my ~20" (cube) subs. Then placed a large pot plant on top of each one. One sub was placed under each of the two windows in the room. This made it look like the subs were actually purpose built plinths lifting the plants into the light. I simply painted the MDF boxes matt black so any water damage from accidental spills wasn't a problem. Those with wood finishes wouldn't want to take the risk with plants. Find a suitably large table lamp to match the size of your own sub.
Think about your pine chest for a moment. What makes you think it is acceptable as a chest? But not as a similar sized subwoofer not pretending to be a chest?
Remember light colours and light wood finishes make things appear much larger. Black is okay perhaps with a bit of camouflaging cloth. While white is always HUGE!
NIMBY