Abstract: A filament wound composite tube is inserted into a non-metallic mandrel below the core to support the core when holding pressure in the top annulus. The tube has a close-fit tolerance to the inner surface of the mandrel. The tube is secured in place with pins through a mule shoe, such that the bore of the tube is not impeded. Alternately, a retainer with wickers is disposed in the mandrel below the core to support the core when holding pressure in the top annulus. The wickers are biased to engage with an inner surface of the mandrel, holding the insert in place under pressure. Axial movement of the core downward further engages the wickers with the mandrel, helping to support the load.