Trickle vents are an easier item to fit for a diy'er than a permavent, and a quick visit to a local pvc manufacturer will show how easy its done.
Normally an overhead pvc milling machine roouts a slot in the frame approximately 10mm wide, and whatever length the vent is approximately. The vents are then installed with an external cover vent, and the internal control vent. It is possible to retro fit these, with out routing, basically drilling holes instead. best to get exact fitting details from the supplier.
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