What's that smell?

Can't say for sure what the smell is but it could me mould.... I really do hate to say this, but your trailer may have alot more damage than you think. You probably would have been better off walking away from this one, unless of course you got a great deal and don't mind a project... If the wall is saturated the enclosed underbelly will more than likely also be saturated. This is likely what has caused the soft spot by the door. Unfortunately there will be more damage that you can not see, including mould. The best thing you can do is get things opened up that are wet and get them dried out. The inside of the walls and floor will only get worse if they are not opened and dried out. simply putting heat to the inside will not dry things. This is alot of work to take on.... I have been through this personally and it takes the fun out of the whole RV experience.

Good luck