Select all perimeter of your hole
Make Network
Select All : Boolean Union = you have a solid ;)

If surface result is not suitable for your wish you must extract perimeter of 2 general curves of this surface and edit it!
Here a possible edition...Trim the surface and make a Sweep...


But in this particular case as your model is symmetric better to take a middle of the space ship and make a mirror! ;)



Seam don't appears with material...