Itasca Sunstar 31KE Rear Wall Rot

[corton]

Getting ready for our first long trip in the RV, I found something I never noticed before. This unit is a 2016 purchased used last fall. In the aft compartment, where the bolts to hold on the bumper come thru the rear wall, the aluminum is basically rotted away. I checked the gennie closet, and same thing there.


Known problem? Just put a big fender washer over it, and seal with FlexSeal (tm)? That's pretty thin aluminum, and it appears to have structural foam just behind it. No looseness, just disturbing...


Thanks for suggestions.

[SLOweather]

I just checked our 2014 31KE. No real sign of rot (yet), but they do look like the nuts were maybe tightened a little too much, crushing the plywood.


I'd guess that the bolt penetrations through the wall were not adequately waterproofed, allowing rain water to wick along the bolt shafts. I had the same issue with some P.O. installed equipment on the roof wicking water along the screw threads and rusting the screws.


Now that I've seen this, I'm considering loosening or removing all of those bolts and sealing the shanks and spacers with butyl tape.


It would be instructive if you removed at least the worst bolt and told us how it looks.

[corton]

I'm willing to do that, but haven't checked it out yet. I was (ignorantly) assuming the bolts were actually attached/welded to the bumper itself, so I don't think I'd be able to pull out one bolt without removing the entire bumper. Getting ready for a trip so really don't want to do that until our return. I appreciate you checking on your 31KE!

[SLOweather]

I just checked under the whole back lower edge. There is some corrosion there, on that aluminum backing above the bottom channel. It almost looks like electrolytic damage.





I think it can be cleaned up and then sprayed with undercoating, Plasti-Dip, Flex Seal, or something similar.


Some, if not all of my bumper bolt spacers were sealed with something. And the bolt heads are slid into a C channel on the back of the bumper extrusion.


So, one would have to either remove all the nuts and then pull the whole bumper off, or, perhaps, loosen them all and then slide the bumper off.

[SLOweather]

I got under there just now with a brass brush and started brushing the corrosion off. That thin aluminum panel has corroded away down to the plywood in spots.






I'm off the Harbor Freight to pick up a can of rubberized undercoating to seal it after I have finished brushing and cleaning it.



Thanks to the OP for getting me to look at this.

[SLOweather]

BTW, that F53 chassis on 19.5" tires has lots of room under it. I can scoot around all of the underside on a 40" Harbor Freight creeper easily. About the only things I can't go under are the drive train and exhaust system.