Yes, pine would last that long.
If possible use 2x stock, use screws in the corners, plus
plug the screw counterbore holes.
Also, because of the length-width, put in some braces mid-way,
or third of the way to stop the beds from bowing out.
Alternatively, stake the bed into the ground.
If using glue along with screws, use an exterior or marine
glue. The powder kind where you add water works quite nicely.
Think thrice, measure twice and cut once.
Sanding is like paying taxes ... everyone has to do it, but it is
Click to see the full signature.