Hey Jon,
For the corners: I would recommend fiberglass bondo filler. Sand and wrap with a vinyl or spray paint. We did this on ours and it's working very well.
Hey Andreas, I started down this path but small cracks appeared along the seam between the Bondo and Aluminum plates. My current plan is to do this same process but then wrap a single layer of fiberglass cloth over the whole thing, fair and paint with Sem Satin Black Chip Guard paint. An extra step but I think it will take care of the problem.
Another update, pretty much finished building the rail that will contain the top of the seating area cushions. The drivers side will have a small wall parallel with exterior wall. This moved the seating area over a bit to make getting in and out easier past the counter top. It also gives a little storage and space for the water hose fill and vent. There will be a 45 degree vertical board in the corner above to provide a wire chase and mounting point for the led reading lights.
Next to the heat exchanger in the foot well I will put in an AC outlet with dual USB chargers.
This photo is a bit fuzzy (camera phone) but tries to show the maple laminated bathroom door frame. I removed some of the honeycomb coring all around the opening then Sika 252'd in strips of wood flush. Then bonded/glued thin strips of maple, bending around the corners. I plan on using the door cutout as the door with cast stainless hinges. This is fussy slow work but I think will look good when finished.
This is the LifePO4 400ah battery bank in a 4P4S configuration. I have ordered the cell balancers, bus bars, cables etc, once that stuff appears I will use it for filler work. It is getting pretty hot here, pushing 100 with high humidity, so dragging a bit by the end of the day.
Still waiting on hearing from the welder, starting to get the feeling I might have to press ahead and try a bit of DIY welding. We will see in about 3 weeks when the interior build out (minus the wiring/plumbing) starts to slow a bit. Really would like to get the solar panels mounted, but the mount needs fabrication as I want to add rails along the edge to protect the panels.