I don’t know what fabric you’re using, but assuming you’ve tested the welds and you’re satisfied they’re strong, then if you’re careful to avoid leaving any gap where the two pieces meet then it should work out fine. You can’t heat seal a fabric patch over Seam Grip though (or to the inside of the tube fabric, for that matter); instead, I would use Aquaseal to cover the area, both inside and out (Aquaseal is more viscous than Seam Grip so it’s better for patching tiny leaks).