IM sure its sealed well.
im just envisioning you trying to pour foam in the ski using the same half assed technique you used for glassing these in!
haha
let me guess, you didnt want two part foam, you will use 'great stuff foam'?
haha
im messing with you man.
it will work, it will be fine.
you really though, missed some key info in your researching and reading of "millions" of threads.
spend more time reading, and less time posting.
[ I dont mean that as mean, or an insult, seriously though]
there is a LOT of good info, and pics here, it takes a while to learn how to determine what is BS, and what isnt.
and YES, I think you didnt prep ( sand, and clean) enough
BUT you keep saying you did, so , time will tell.