Ok, so I read into that I should keep adding sugar until it 'dry'. It just melted into a slather almost immediately.
It tasted fantastic. I'll probably add some more clove, allspice and peppercorns in the brine and in the sugar next time. It was super good, but could have used some more.
I will also get this a try with a proper ham, but damn were the butts good.
Good notes for the future.
Shirley Fabrication 24x60 staightback cabinet + warmer
22.5 Weber OTG