I use Lidcovers from Ridetek, they were easier to put on and the velcro stays put. Anyhow, you need to make sure that once the velcro is installed (proper temp, clean surface) that you allow it to sit like 24 hours without the covers installed and pulling on the velcro. Also, as other have stated, heat the covers.
I had my covers installed by the dealer before I took delivery on my old SG, and the velcro was sliding all over the inside of the lids. I suspect they didn't let it set up for the 24 hours you mention above (go figure, a tech not following instructions?). If it hadn't been for the way the tape kept sliding I'd give them a big thumb's up, 'cuz they sure did protect the tops of my bags.
if they are authentic Leather, DON'T hit them with a hair dryer. It drys the leather and promotes craking down the road.
IF its real leather and not vinyl, then you could get them wet and leather will strech. Wet them evenly, and completly. Don't just get a small part of it wet, as that could leave a watermark. Once on, Let them dry naturally, and then treat them with neatsfoot oil or a good leather Conditioner.
Mine were on, I used a heat gun, then after a few days they reshrunk and came off! There sitting on the bench in the garage.. Ill give them another go when I have a few days to keep heating and stretching them.