For indoor use, you could skip the pvc frame altogether and just go with 3 levels of Styrofoam with Styrofoam spacers.
Personally, with a fairly simple design as the GH2n2, I would go with the traditional center pole method. The 2 center sets of uhf reflectors would go into thin tubes (to hold the spacing between them) and then go into a hole in the 1" diameter center pvc post. The 3 vhf-hi back elements would be mounted from tees and pipe in the center post. The front driven element would be mount on 3 sets of tees and pipe from the center post. I would use 1" to 1/2" reducers out from the center post tees to reduce cost and wind resistance. The NAROD to stub separation would be held in place with scrap vinyl siding spacers. The top of the top hat NAROD would be attached to the center pvc post.
I would not glue the pvc joints, but rather use a small #4 screw to hold the fittings in place.
If built this way, using the cheaper grey electrical pvc pipe, it would be durable and wind resistant to use outdoors in the future.