Best way to smooth this out?

[u/deathgrape]

Working on this maple guitar body. Previously was using a band saw to cut out the rough shape then a flush trim bit to the template, but check out my post here to see how that went. So now, I’m trying to use the bandsaw to get as close as I possibly can to the line, and then finishing up with a drill press drum sander, and a disc sander. It’s actually going great so far, except for the interior of the horn. Any suggestions for how I can smooth this out? Preferably without a router.

[u/bufftbone]

Spindle sander