Assembling Ductwork For Range Hood

I am running 7 inch round 26 gauge metal duct for our kitchen and assembling five 3 foot sections for a long run.

When I align all the seams I find one seam on top of another forces the walls of the mating ducts apart significantly. Would it be better rotate the mating ducts so the seams are four inches apart? I find doing this reduces the distortion of the duct walls.

In addition, I am using three #8x1/2†screws to secure the mating ducts together and sealing the joint with UL Listed metal duct tape. Should the seams that run along the length of the pipe be sealed also with tape?

Thank you for taking the time to read my post and consider my questions.

In case anyone is interested. I offset the seams by three inches and inserted one of the three screws securing each section between the offset seams. I used Polyken 339 to seal the sections and seams. I used CCWI-181 on the 90 degree elbow seams.

http://polyken.com.mx/Archivos Polyken/PDF/Industriales Trad/Fichas Tecnicas/FICHA TECNICA 339.pdf

http://www.ductoutlet.com/CCWI_181_Duct_Sealant_1Gal_p/ccwi-181.htm

I built one a few years ago with 8 inch pipe with an eight inch inline fantech exhaust fan. I used the foil backed tape at most joints and seams and no screws. I used neoprene lined clamps at the back draft damper and at the fan motor. The clamps reduce noise and make it easy to take apart and put back together.

http://www.hvacquick.com/products/r...Exhaust-Kits/Fantech-Kitchen-Ventilation-Kits