Recommended to have drain hole in PVC weatherproof electrical box?
Yes, and you'll want a 1/8&quot; hole
This is governed by NEC 314.15:

314.15 Damp or Wet Locations. In damp or wet locations,
boxes, conduit bodies, outlet box hoods, and fittings shall be
placed or equipped so as to prevent moisture from entering or
accumulating within the box, conduit body, or fitting. Boxes,
conduit bodies, outlet box hoods, and fittings installed in wet
locations shall be listed for use in wet locations. Approved
drainage openings not smaller than 3 mm ( ⅛ in.) and not
larger than 6 mm ( ¼ in.) in diameter shall be permitted to be
installed in the field in boxes or conduit bodies listed for use in
damp or wet locations. For installation of listed drain fittings,
larger openings are permitted to be installed in the field in
accordance with manufacturer’s instructions.

I would not seal the rest of the box though; the idea with normal weatherproof electrical enclosures is to provide a rough seal to keep bulk moisture, bugs, and such out, while having enough air movement to prevent any pressure differentials across the seal from driving moisture in through the slightest imperfections.  (The drain hole helps with this as well, although you'll want to keep an eye on it as spiders can be particularly pesky hole-pluggers.)