ETA - just thought of something else. If the nappies you're taking off aren't completely sodden, you might get on with a fleece lined nappy. Something like a Bumhugger that already has a stay dry layer in it might suit you better. Brain addled and I can't think of others OTTOMH, but I'm sure there are more. A Bumhugger is quite slim as it's all hemp, so does stand up well to heavier wetters.
why do you say that? what are the technicalities there then?