At 3-6 walls thick they shouldn't be brittle (they're 3 in some areas, supported by a framework of 5-6 wall thick reinforcement in other areas). If you're having issues with brittle/cracked prints in areas that are 3+ walls thick, you may be having extrusion issues or your filament may be humid (moisture causes most filaments to bubble and pop)
if you're worried you can also coat the inside in plasti-dip or similar material (which can sort of self-heal minor cracks)
Any ridged headbase will not be indestructible without being extremely thick/heavy (be it 3D printed, resin cast, or fiberglass/carbon-fiber) so if you want a base you can step on, you'll need to use foam.