Trying to see if my thinking is correct

If I need to glue (2) 2'x3' 3/4"thick MDF rectagles together to make a 1.5" thick sign to carve and paint I can just glue two sides right? This is for a under canopy sign with no direct exposure to sun or elements.

If so is there any prep I need to do prior to just adding some glue and clamping together beside making sure there's no dust?