Not sure that adding down trim is a good idea. If your plane is trimmed you should be able to make it fly straight and level at any altitude. I have planes that I can do touch and goes with at full power because they are trimmed out completly. I fly alot of scale planes so flying to the runway is almost always a needed skill for landing. The down side to high speed touch and goes is I buy more wheels than most RC flyers and I usually have to clean rubber chunks of the bottom of the wing. Practice your approaches and good luck, Dave