ORIGINAL: fix-n-fly
If your LT-40 really weighs over 7 pounds, you are going to find out two things really quickly: 1) the front nose gear will bend at the first bad landing. 2) the rear gear will spread out (and stay that way) at the first bad landing. I love the LT-40 powered by an OS FP .40 - had plenty of power for training. Built one years ago, but Sig landing gear is notorious for bending as the metal is soft. If you teach takeoffs last, you could get away with conventional gear and less weight (just a thought).
I had a NextStar Select that had a .46 engine. That RTF weighed well over 8 lbs, yet it flew just fine, for what its worth... All main landing gears deflect on hard landings. This action saves the fuselage from major damage while learning. At least twice, I punched a hole in the bottom of the fuselage from the main landing gear deflecting up into the fuselage. Yes, it was a real noobie landing BUT that is why you fly a trainer.
Another great trainer is the 3D Hobby Shops EBT. It is extremely light and flies like a dream. It would be a snap to learn with this trainer. Make sure to tone it down using low rates and expo for first time pilots, though. It has a very big elevator for a trainer. I actually fly it on high rates and do snap rolls and 5-foot diameter loops...yes, 5-foot...as many in a row as the battery will allow. It flies superb!