Exhaust System Leaks


Wondering if anyone had any tips to seal up exhaust leaks? I put in the GN1 3" exhaust system and it looks awesome but when i ran a smoke test on it (plugged one tailpipe, pumped smoke into the other, every band clamp i had was leaking, especially the band clamp between the test pipe and downpipe. I've seen putty and tape, but wasn't sure if that was for a temp fix, also seen copper rtv that some have used. I'm assuming the best two to seal it all up is take it to a shop and get it welded, but just want to see what my options are in the interim.
Any exhaust leak after the turbo are not going to hurt a thing. If the test pipe to down pipe connection leak nothing negative will come of it.

The exhaust system leaks that are critical are:
-the exhaust manifold/header to cylinder head
-any cracks in the exhaust manifold/header
-Turbo to passengers side exhaust manifold/header
-cross over pipe and it's connections to both the drivers side and passengers side manifold/header

Basically any leak before the o2 sensor or turbo are possibly going to cause problems. Once the exhaust gasses pass the o2 sensor and turbo it doesn't matter if there are exhaust leaks. Now if you have a wide band o2 welded into the down pipe and there is a large leak at the down pipe to turbo connection that can cause inaccurate wide band o2 readings.
Copper RTV works on headers, should be good. If its not a bad leak, anti-seize could work also. I use anti-seize to seal my downpipe to turbo but those are machined surfaces.