Help with level boundings

Hey guys i'm back with another question.

I'm starting my fourth game but i'm running into a problem with the boundings of my level.

I want an object to move around within a tube which is under the ground. But what is the best way to set the bounding boxes, because ican't do it with the collision pylogons because then you have to many.

I thought of putting transparent images around the tubes and set them to solid.

here is a image of how the level look

db.tt/cqmCRY33

place, stretch and angle some basic square sprite to surround all your tubes path

And set them to be invisible

Yeah thank you, i've been doing that.

ten levels to go!