I can't really do them that well on trampolines. I've only tried a few times. But I've tried some into water. Like with my back turned to the water, so its like a switch backflip.
I tried one on skis last season. I didn't land it but I got the rotation. The trick is really just to commit to the flip. If you have enough air time to spin and you throw the rotation reasonably hard you will be fine. I plan on trying some more this season. Also, its could to be able to imagine yourself flipping backwards. By doing backflips into tramps and water you get the feeling for doing a backflip.
no offence but i cant see how kinda good at tramp if you cant backflip