Anyone who recognized them, could solve them. So a dropped axle was used. Bigger wheels make fewer revolutions to cover the same territory. Their bearings last much longer than the small wheels found on other trailers. Witness all those disabled rigs you see along the highways.
Bearings warm up in use.
Sudden submersion cools them, creating a vacuum that sucks in the sea. So we added pressure caps. Bolted fenders can loosen and fall off. So we welded them on. Aluminum construction is expensive and has to be massive to equal the strength of steel.