Regarding dipping, there are two companies I have looked at. Surface processing Ltd and Envirostrip. they both offer a similar service, paint removal, then rust removal. SPL also offer E-coating, an electrolytic paint deposition process, but it's far from cheap.
Envirostrip will paint the body in an epoxy primer, but unlike e-coating that won't get inside any box sections and between flanges. The Isetta is single skinned apart from the door, so less of a disadvantage perhaps.
From what I've observed of the process, it only removes rust, not good metal. If your shell is badly rusted, then it's likely to come out with perforations, but my shell isn't in that category. It was mainly the floor and a few small areas that had corroded to the point of holes. The floor is being replaced, and the remaining areas will be made good.
The majority of rust is just scaly type from years sitting in a damp environment. Easy to clean off with shot peening or dipping, but can be very involved when trying to sand it off.