All of this cartridge building entails a bit of "experiment of one", and one needs to see what works best for one, as always. Wet or dry patches for slicks? Try both, see what works best for it all (the cartridge, the gun, you - and numero uno is consistent accuracy).
After some years of messing around with .45-70 PPB cartridge build processes and their components, I use a BACO JIM444530E cast at 1:16 alloy, wrapped in Seth Cole 7#, the cleaned inside and out just fired and not sized Starline brass (new brass is reformed to fit the custom DT/BD PPB chamber - standard .45-70 brass will not fit) that's initially had it's flash hole reamed is drop filled with 80.5 grains of digitally weighed Swiss 1-1/2F for case compaction, a .060" LDPE wad on top, lightly .060" compressed (on the die press, for consistency).
The dry wrapped PPB slips .1" into the case mouth, on top of the LDPE wad, and is loose enuf to wiggle around and fall out. It goes onto the press and a modified Lyman .45-70 taper die just barely squeezes the case mouth to barely hold in the PPB when the cartridge is held upside down by its head - the PPB is loose enuf to twist around, be removed, be twisted back on and still not fall out.
Upon firing, bullets shed their paper like confetti and punch clean holes in all paper targets from 200 yards to waaay out there. I don't see any way that the dry paper would travel downrange with the slick. I have never been able to recover a fired slick, but I'd like to, and will work on doing that next year. I have experimented with lightly rubbing the paper of a finished cartridge for water resistance during precipitation days at the range and it seems to work without hindering accuracy. ALL fired brass is annealed before reloading, always. To me, that is an important step. In fact, all new brass is annealed before reforming to my .45-70 PPB chamber.
Part of my just-fired case preparation is to check each one for growth. I have and use a dedicated Wilson micrometer trimmer and it might take 8 to 10 firings before an estimated .0001" needs removing. I'm WAY more interested in case interior cleaning than its exterior and the only cleaning device that does that inside of 30 minutes is an ultra-sonic, using Hornady brass cleaning solution. Part of all of this is how cases are handled immediately after firing. I always want to mitigate BP residue from Everything ASAP. YMMV.