Prime bottom edge of bathroom door enough to stop swelling?

[Albumen]

After fitting of landing carpet the bathroom door is catching on the door plate.

I've taken it off, and planed a bit off the bottom.

Before I re-hang it I thought I'd (at least) prime the bottom edge.

Questions:

1. Do I need to paint it at all? It's the bottom edge, the top is already painted. Not sure if it will absorb a lot of moisture. And at least one internet suggestion is that leaving it unpainted allows moisture to get out as well as get in.

2. If I do need to paint it is oil based primer enough to seal it? Given how long gloss takes to dry I don't want to leave it off too long.

3. There will actually be a fairly big gap under it, at least in the bathroom. Any tips for painting it in situ? Pads or something similar?

Thanks

 

[Robbie uk]

Personally I wouldn't bother painting the underside of the door. I doubt it would ever make much difference to the swelling of the door.