Matte paint includes a “flattening agent” which replaces a bit of the pigment and binder (the glue) ... All Latex paints in a thick coat will take a week or more to really harden ... older
may take longer ...
From an artists standpoint , we’ve been working with paint for over 50 years now ... You can paint the interior Latex first , and then cover over it with an Exterior Latex ... I believe the Exterior paint has UV inhibitors.. and the better the paint ,the more UV inhibitors (and anti- fungals, etc. ) the better it will last in the Solar radiation and weather extremes ...

Cheap paint is fine for a base coat ... as long as it’s protected later on ...
Note : for the large Portrait commissions I do , we save the very Best paint (Old Holland) for all the sweet spots in the painting , otherwise I’d have to charge double just to cover the paint cost ... The "block in" and background is painted with the less expensive product.
Paint for trailer , best exterior Latex.. ~ $35.00/ gal ... Artist oil paint ... ~ $35.00 for a small tube , no bigger than your thumb.
Use the best paint you can on the outside , or keep it in the garage when not camping ...
