Hi Bob,
I was thinking of the 18" drum also... primarily because I could get small box pieces, etc. over the slot & sand them where the larger slots would make it more difficult if even possible. (I even got to thinking about a jig placed over the drum for very small pieces!

)
At one time, I was thinking of scrounging the parts, pillow blocks, shaft, pulleys, etc. & even making the drum out of individual cut circles, etc. ... BUT, recently, I figured it wasn't really worth the effort as well as taking a huge chance that it wouldn't work good (as good as with their parts). So, I've decided to just get The Works kit for the 18" unit.
That way, most of the critical stuff will be done for me!!
It has been a long time since seeing the Mop sanders... thank you for bringing those to my attention!! They're cool too!! Although I couldn't find the Dremel sized goodies on their site... guess I'll have to call them... The 6" combo of 120 / 220 looks good to me.
They used to have another video, that I thought was better than this one... showed the ease of changing drum grits, etc. and even setting up more than one grit on the same drum!! This is COOL stuff!!
Caution... the prices, shown at the bottom of the videos, are Canadian... US$ are LESS!! I'm glad I noticed that!! (cause I thought it was getting a little Pricey... More reasonable with the US$ price!)
Keep us up to date on your progress... OK? I will do the same.