When I make my panels I usually use 1/8 in. standard masonite or pressed wood. You can also use 1/8 in. birch plywood or gator board which is found in art stores. When buying masonite or pressed wood make sure to buy the standard as opposed to the treated panels which are injected with a petroleum substance and are darker in color. I use Elmers all purpose glue from the hardware store, a 2 in. inexpensive house paint brush and a kitchen rolling pin. After cutting the boards to size I cut the canvas 1/2 in. bigger so it can be trimmed. I dampen the bush to make the glue spread easier but don’t add water to the glue, it weakens the bonding strength. Spread the glue evenly on the board then press the canvas on the board. Use the rolling pin to roll out the air bubbles.
I usually prepare a number of panels the same size then stack them and place a larger board over all of them and place a 10 pound dumbbell to weigh them down. I generally let them dry overnight then with a sharp utility knife I turn them over then trim off the extra canvas. If the corners come up I apply a small amount of glue with a small brush and press down.
For panels larger than 16 x 20 use 1/4 inch panels and gesso the back to prevent warping.