I recently fixed a popped seam on my GC3. I had restretched the cloth when doing this and the 1/4" of movement I had when making a brdige was thankfully now gone (I used a canvas stretcher). The table is in a room with no a/c but it is winter in Jamaica and our humidity is nothing like what you find in the USA. I keep the table covered ALL them time unless I'm playing - it is covered back up immediately after playing. The tension in the cloth was holding up nicely for the first few weeks. I got lazy and left the cover off for about a week and the cloth started to "loosen up" again. I was pretty bummed and I began using the cover again. The cloth "tightened up" by itself again and has been holding tight since. Maybe one of the mechanics here can offer an explanation and hopefully anybody who has the same problem, this can help them. I'm just guessing the cover just keeps out the humidity....