In article , no-
says...

I want to add a couple of bolts/deadlocks to the inside, how easy is this to
fit to uPVC? Would a heafty dollop of "no nails" and a few 3/4" self tapping
screws be enough to secure it?

Cheers
Mike

No.

You might want to consider "thumb-turn shoot bolts" or "finger-operated
shoot bolts" if your doors don't have them already. (Should be fitted as
standard on French Doors) They can be retro-fitted in the eurogroove on
the edge of the Master and Slave doors.
They work vertically to engage a pin into the head and foot of the frame.
Cheap to buy, easy to fit.

A Google search will produce several references. The Fullex web site
could show examples.

HTH

--
Ziggur

"S'ils te mordent, mords-les"