Well, the trainers we see around here are usually the Alpha, Hobbistar/NextStar and LT-40, all of which have flat-bottom airfoils. The Arrow from H9 has a semi-semetrical airfoil, but the incidence agles and thrust line on that plane are a mess to try to make it fly more "trainer like".

Oh, another trainer-acrobatics trick. Raise both ailerons a little bit. That "reflex" will often reduce pitch changes with airspeed and can really help inverted flight.