Reverse Solid

I'm trying to make a game with a moving ship, top down. I want to make it so that the crew can walk around the ship but not off the ship. Is there any way to create an "inverse solid" or a "can only walk here."

I've tried setting the background to solid, hoping that the ship would provide a walkable area, but it didn't.

I suppose I could pin walls to the ship but since I want the Player to be able to build his ship out of pre made blocks, that would result in multi-layered pinning (which in my experience lags).

Please help, I can't figure out how to do this.

I guess this behavior will be useful for you?

Link:

scirra.com/forum/behavior-runaway-sprite_topic53232.html

an "inverse solid":? that is basically anything that isn't a solid...so just solid the walls?...use tiled backgrounds or sprites with with solid behavior added or restrict the movement of the player with x and y, ie player.x >500 set player.x to 500