The weak point rot-wise will probably be the grooves between the
boards on the lower part of the doors. Water finds its way into the
t&g joints where it can't easily evaporate.
There is *something* to be said for coating all the components in wood
hardener before assembly, including the individual tongues and
grooves, although the colour would need to be established beforehand.
It effectively applies a thin film of hard plastic.

I'm not familiar with the stuff. Is it significantly better bet than wood
primer for this purpose?

It's designed to soak into old, porous timber and effectively convert
the fibres to plastic. On new wood it's more likely to sit on the
surface, but my limited tests suggest it beats the hell out of anything
else as a sealer. I've always painted over it so I can't comment on how
it would respond to UV exposure in a transparent finish.