This is an interesting idea and could be alot of fun.
Would you limit the amount of stuff the player could mod though? I think you should other wise you'll have players modding 10 different hull sizes with 20 different weapons to put on there. While another may mod 12 hull sizes and only 12 weapons.
Even though the point is sort of a god mod thing going on here I would think you would limit how much they could mod.
Say for instance you set a limit of 7 new weapons.
3 new hulls.
and so on and so forth.
Just a thought.

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Ragnarok -
Hevordian Story Thread
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I think...therefore I am confused.
They were armed. With guns, said Omari.
Canadians. With guns. And a warship. What is this world coming to?
The dreaded derelict dwelling two ton devil bunny!
Every ship can be a minesweeper... Once