Rotten bottom step

[Gringo]

I bought our 1998 aautrail cheyenne two years ago we hadn't had it long before the bottom step was water logged i replaced the step and put a new seal on he door and resealed round the outside which seamed t o sort it but it has started to leak again but I can't locate the source . Any suggestions would be appreciated it was stored inside by the previous owners now I know why

 

[Wombles]

Bump - can anyone advise?

 

[Jamesh]

Pics??