What about a wool portal thats goes form water level to the sky?
Ocean Level is the elevation 63 (
look here) and we can built )... I don't know what's the level of the sky where we can't put anything, we have to count it, I can also do it for you.
Then we have to use wool and calculate dimentions...
We can aslo do somthing like copying the real portal and do it 1:8...
So, a normal portal is 4*5*1, our wool portal will be 32*40*8... Do we have 40 spaces from sea to sky?
If we don't we can do also 16*20*4, or others...