Bent Door How to Straighten?

[RV Bummin]

The main door of our Motorhome appears to be bent. We bought used, but the former owner does not recall anything happening to the door.

The bottom half does not fit flush with the frame as though something or someone pushed it out at some point. I have tried to bend it by placing a 2 x 6 edgewise between the top of the door and the frame and pushing on the bottom of the door. This did not work, perhaps due to my old muscles being too weak.

Is there a trick or a proper method of straightening a door? It lets cold air in, whistles and creaks etc.

I hate to break it for good as it functions OK, just half of it does not fit. It sticks out from the frame almost an inch at the bottom.

Any sensible advice would be appreciated.