Has anyone changed the seal on the door frame of their caravan?

We have recently bought a second hand caravan and find the rubber seal on the inner door frame has been bent and folds inside the hinge of the door when closed, thus breaking the weatherproof seal and allowing rain to come in onto the step of the van. I have tried to straighten the seal but it keeps going back to the bent form it's obviously been in for some considerable time. First of all, is it possible to straighten the rubber seal, (I'm a bit apprehensive to apply heat to the rubber) and if not, how difficult is it to replace the seal or would it need to be done professionally? I would appreciate any comments/suggestions you might have. Thanks