More than likely there was some damage done to the tubes during installation. It's really easy to get a part of the tube pinched between the tire bead and part of the rim. Even a pinch between the edge of the tire bead and the bottom of the rim will lead to a blowout. Adding a small amount of air to the tube before mounting can help a lot. What I can blow into a tube using my mouth is about right. Too much air can add to the difficulty.