Already converted rear window but I don't think it saved much weight... the rear glass is very thin / light
Going with something like this for sealant
Permatex 24105 RTV Silicone, Oil-Resistant, 13 OzCart, Blk
... the piece is cut to the precise dimension of the OEM glass (so I'm told!) and so was planning to use the OEM frame with this RTV sealant... 1/4" polycarb is I believe the same thickness so fingers crossed it will all work out
I may also chicken out and call a glass guy in to do the job! haha