To save disk space, you can use /db purge.
I’d place or remove 9 blocks right next to the trader, then use
/db purge 8
That’ll get rid of chunks without at least 8 modified blocks (or 8 or fewer, not sure) in them from the DB, to save space. You’ll need to use /db vacuum to actually free up the space.
I find I need to run /db purge in dry run mode first, or the server crashes, but YMMV.
[ Sorry if the commands aren’t quite right, I’m away from my VS computer. /help db should steer you in the right direction. ]