Line ( braid ) slip on multis can be confused with the drag ,I have used multis for the past 30 years, so have more or less got them sussed. One of the best ways of preventing line slip, is to wind on a few inches of double sided sticky tape onto the spool spindle, then if you prefer , back the braid with mono. I never bother using backing, I just tie the braid onto the spindle with a Uni knot, and tightly wind on the braid until the spindle is completeley covered. This method is used by Tarpon anglers in the USA, so here in the UK we will have nothing to compare with those mighty warrior fish in the guise of Pike.
Backing with mono is perfectly acceptable, but make sure everything is wound on tight.As for spooling the braid,as already stated, put the braid spool in a bucket of water, then wind onto the multi through a bit of towelling or similar, it keeps the water splashes at bay, and beds the braid down niceley.
Keep everything tight is the key.
Dave