My raft (Survival Products) weighs about 10kg.
I am curious about the "one wing full and one empty" issue. On my TB20 I can feel a noticeable roll tendency (needing constant aileron input) if the tanks are only a bit, say 20USG, out of balance. So, using the accurate fuel gauges, I run them reasonably balanced but with about 3mm extra on the RH (as seen on the gauges) if flying alone. A complete full tank one side would be most noticeable, unless one had aileron trim, used it blindly, AND never even looked at where the ailerons are sitting.