In the mid 60's there was no frame over the skin surrounding the door. It is a nice smooth look, but the door seal is the ONLY thing that is going to stop water from getting in. Newer models have a rain gutter on top, as well as a frame to help to divert the water. New seals should take care of the issue. If the floor is not too far gone some rot doctor shoudl fix it and save you from having to do a ton of tear out.
I would check the vulcem over both of the curb side windows. The soft spot further forward may be from the door leak as well. If the vulcem is cracked or gone I would start there to fix this one. Also check the awning rail or any awning mount points high on the trailer. If silicone was used it has failed and will need to be replaced with vulcem. Chasing leaks can be a challenege, but it is satifying when you get one fixed.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato