My cardboard Titanic is almost complete, and...?

How to waterproof the ship so it can float on water? Especially the loose joint between the windows? Is using silicone rubber sealant is good enough for waterproofing the ship...right now, I'm using Hardex Silicone Rubber Sealant for the sealant, is that enough. Any kind of help is very pleased, thank you in advance.
 
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