To magnetize your Command Barge and Annihilation Barge, use the Large Posable – Medium. The flight stand will sit near the middle back in the hole and you need the extra height of the Medium.
[Buy Product=large40k,variant=all]
For a peel-and-stick option that works with clear flying bases, use the Peel & Stick Inner Base Magnets — no drilling required.
[Buy Product=flexible-self-adhesive-magnets,variant=51483453948194]
For a replacement base use the bases with magnets that have holes preset into them.
[Buy Product=bases-premagnetized-warhammer,variant=30427499626580]