If you need to inflate/deflate sib constantly at a beach, lake, pond, whatever. You could spray a liberal amount of soappy water all around floor fabric and under keel. Include side stringers, joinners cuts, will slide at a snap onto floorboards sides.
Soappy water will help to slide all floorboards nicely inside lower fabric, once correctly positioned, align keel valve. The issue of inflating with bow up (someone could lift bow up using front handle) is for keel to find its way under assembled floorboards as opposed having all floorboards compressing the keel downwards.
Alternatively you could inflate keel once sib is floating with hand or foot pump, that will depend if lightly or heavily cargo loaded.
Try any of the tips and check which suits you well, all have worked ok for me.