I have an extra mech hangar that I throw a variant into that I know I will need to unlock for Master level Pilot on my Primary. Once I have unlocked all of the Master boxes on the second model, I will sell it and repeat on a third model. Sell it and go back to your Primary, and you will be unlocking Master in no time! I'm almost done with my CPLT-C1 (Master lvl), moving on to my VTR-DS Dragonslayer, now!
My current hangar includes: RVN-3L Raven, VTR-DS Victor, CN9-AL Centurion, JM6-S Jagermech, JR7-D(S) Jenner, CPLT-C1 Catapult, BJ-1X Blackjack, AS7-D-DC Atlas, + (empty hangar).
Waiting on Project Phoenix to get here, then I'll have my own 'Reinforced Company'!