A recent thread on a garage roof reminded me that I really need to tidy
up my (warping softwood ply) garage doors before winter...

The sizes are 1.1x1.7m and both open outward rather than a single up and
over.

I was thinking of something fairly quick and cheap, ledge and brace, or
exterior OSB back panel and vertical T&G front boards (I don't care what
the inside looks like).

WRT the OSB idea, this will give about 40mm thickness, which is about
right, but are the panels likely to distort much?

Has anyone got any other ideas that would match in with a shiplap clad
structure and are reasonably quick to make / cost effective?

TIA,

Alex.