There is some great information in this thread. Thanks for sharing the bushing info. I like the idea of making and installing the “Doublers” that go on the backside of the tub skin. I plan on beefing up my tub skin when I do my tub overhaul in the future. For now mine is OK, with the little OEM wheel & tire on the back.
Something I will suggest, to help make the installation even stronger, is the use of structural adhesive, while assembling these components. In the aircraft sheet metal trade these are referred to as “Fayed Surfaces”. All “fayed surfaces” go together “Wet” with structural adhesive while manufacturing and repairing aircraft. The structural adhesive is very strong and will fill voids or gaps when parts don’t meet, or line up perfectly. Structure adhesive when cured is soft like rubber, and amazingly strong, it is not brittle like other adhesives. Structural adhesive also provides a barrier, that will seal the parts preventing corrosion.
Mix a batch, apply it to both surfaces that will be in contact, and then install the part. If bolts are used, dip or coat the bolts before installing them. Each fastener should be coated before installation. When the fasteners are installed, excess adhesive will be compressed out on the edges. If you wet install a doubler, it will have superior strength and be resistant to corrosion, that’s a win/win.
MIL-PRF-81733 sealant is the preferred sealant on military aircraft, because it has corrosion inhibitors. I bought a kit of 3m structural adhesive for about $20 if I remember correctly. Your local Napa store can order it for you.
When I repaired my windshield frame, after my wiper linkage failed and bent the sheet metal, I used structural adhesive when I installed my doublers. This stuff will stick to anything, and is very strong. Once it has cured, you would have a hard time removing any part that was put together with this stuff.