Here's our recommended post-core-buildup procedure.
I use posts not just to help retain buildups, but also to add strength to the prep, which helps prevent horizontal fracture. This technique gets a thin resin bonded to the post (the resin in Surpass 2) so we don't increase the thickness of the post, and gets resin bonded to the canal and chamber walls. Then the whole internal of the tooth with the post about 1/2 way down one of the canals is a "uniblock" with some flexability due to the elastic quality of the post and the composite. May be a bit controversial but in addition to this technique helping to retain buildups, it's also reduced the number of horizontally fractured endo teeth significantly for me. Hope this helps.