Have you seen this gimbal? It actually seems to do quite a good job considering the price http://www.aeroxcraft.com/index.php?...&products_id=5
You might need to extend your landing gear a bit though.
If you can afford it, then you can't go wrong with the photohigher gimbal and it will be better if you upgrade your frame in the future. The problem is that to fit it you need to find an extended landing gear for your F450. There's plenty of them about though, so shouldn't be too difficult finding a suitable landing gear.