When doing a cloth backing, its a good idea to wash the cloth with soap, rinse well, and dry. That way the cloth will shrink if it needs to, and their will be no oils or other contaminates to interfere with the glue bonding to the wood. I have used canvas backings and I've not had any problems. Masking tape makes a cheap clamp to hold the backing in place. The TB glue will set-up under it. After a few hours, remove the tape and let the glue fully dry.