The annoying bubbling under the doors seems to be quite a common thing. I suspect/guess that the bubbling might be anodic corrosion rather than a surface issue. Caused by the steel running board fixing screws piercing the return skin of the aluminum bodywork. Water could quite easily enter the running board joint and kick this process off.
I've taken some preemptive work on mine to better seal the joint and have replaced the steel screws under the door with aluminum screws.
![[Linked Image]](https://dl.dropboxusercontent.com/s/znpghejnr8d7j6n/ali%20screw6.jpg)
![[Linked Image]](https://dl.dropboxusercontent.com/s/zfzwutoome5m1wr/ali%20screws7.jpg)
Who knows if it will do the trick or not but a couple of hours investment may well be worth it long term. So far so good.......
