I have 8 of these suckers to paint. They are the cheapie $19 a door ones from HD/Lowes and are being used as sliding doors on basement closets. They have been hanging for a year now with nothing other than their primer coat. I see no signs of warping or anything so, though cheap, they look decent and seam to serve their purpose. I figure I should paint them.

Let me say I painted some 6 panel doors upstairs in the past. They were new with the house 20 years ago and likely were better quality. I rolled these and brushed the squares and they look ok but I see stipple. I figure there is a propper way to paint these and I wonder what it is and what tools I should use.

so...

Should I paint these while hung or lay flat?

Do I need to paint both sides since they are primed and being sliding doors, no one will ever see the inside anyway?

Brush them, roll them or both?