I make easels from melamine covered board. Screw 1/2 inch square battens to 2 sides ensuring exact right angle at corner. With permanent marker, outline paper sizes you will be using. Spray with 3M Spraymount (not Photomount which is permanent). After composing image insert paper into the right angle corner and smooth flat with edge of hand. After exposure lift free corner with fingernail; it lifts easily. When stickiness fades, re-spray with Spraymount. When surface begins to look grubby, clean with white spirit (turps substitute). I have been using this method for 30 years.
Incidentally melamine board does not come in convenient thicknesses for auto-focus enlarging; if you have a Focomat you may need to build up base with thicknesses of 1 mm stiff board to get desired height.