surface modelling - network of ducts

Hello everyone

I'm trying to model a network of ducts in surface modeling. I have managed to do so, but when I try to add thickness to it, doesn't work. I later understood that its cause of the minute openings between each surface. I have attached the model for your reference and to better understand the problem.

Would appreciate your help in resolving this issue.

best

Srinath

SolidworksSurfacing