My expeience with using T's and elbos with PVC is that it weakens the
structure. Dont really like PVC for doing what you are talking about and
prefer to design antennas that will be self supporting and cand withstand
the elements. That being said, There are PVC couplings designed for
transistioning from threaded metal pipe to PVC . For a while I had an
antenna similar to your discription that was set uo as follows. 2 inch
galvanized pipe for a mast, pull box on top of that ,2 meter colinear
array
above that in PVC. Feed line entered through a compression fitting in the
cover of the pull box. This worked well for about 2 years then the sun
began
to cause severe deterioration of the PVC.


PVC pipe is not made for use in the sun. The UV rays weakin the tubing. It
will stand up beter if it is painted or coated so the UV rays will not get
to it.