Under the shelves on the back wall of this coach are just such a problem area. Pondering this, I remembered that some time ago, I'd aquired a Proxxon 28594 power sander and perhaps this might be just the tool for the job.
To be honest, I'm not that good at resorting to power tools - something more profesional modellers do at the slightest opportunity, for speed, and often accuracy. I'll carry on hand working something, partly because the tool isn't set up and doing so takes effort, but mostly because I'm not in the habbit, although I probably should be.
The first snag is that while I'm sure I once had proper self-adhesive sanding pads, these are long gone. No worry, some normal 240 grit sandpaper attached to the sanding head with double-sided tape worked perfectly well - I was soon smoothing away under the shelves and in all the hard to reach areas.
A technique is required - when using the tool, put your finger in the indented area, a bit further forward than you see in the photo. I kept my pinkie back for clarity, and also because I hadn't worked out what to do at that point.
Another thought - use coarser sandpaper. 240 grit is fine, literally, but I could have gone for 120 and been fine.
I've not worried about a second coat of sanding sealer, but the resulting bare wood look works well inside the coachs, so I'm happy, and will try to keep this useful tool closer for future jobs.