Terry Coombs posted for all of us...

And I know how to SNIP


To do it right requires a pretty well-equipped shop - molders , table saw
, jointer-planers , clamps , etc . I suggest you find the nearest discount
lumber outfit and buy a prehung door unit . The expansion/contraction issues
are inherent in wood . A well-sealed and varnished door will have less
trouble than one that's raw . If there's also a security or storm door
that's even better . Don't forget to finish the top and bottom , that's the
biggest mistake DIYers make .

Yes, six sides must be sealed.

--
Tekkie