I would be very careful flying under a CB, Airliners have been unable to cope with some
Absolutely correct. You can easily get downdrafts which a small a/c simply cannot outclimb.
If at all possible, avoid CBs like the plague. And don't get fooled into thinking 'in Europe they are harmless'. They are not, and in some parts of Europe (Alps, Spanish Sierras) you can get stuff that rivals the US.
On a slightly different note, the argument about 'avoiding CBs might put you into CAS' is largely a UK problem. On the continent you generally get CAS penetration/transits very easily and ATC will usually be very accommodating if you explain why you need to do what you're doing. I've been cleared w/o any trouble through mil areas in France while slaloming through a squall line.