25 yrs ago, I bought a Porter Cable 7" disc sander ($180), with a rubber "plate", for heavy sanding (24 & 36 grit discs) in those sorts of areas. It works great for those types of areas, especially when there's a lot to chew away. I've learned to "carve" with it and use it for many other tasks. I've only had to replace the brushes a few times. Don't know if today's sander would be of the same quality.
Additionally, for curved areas, I've made an assortment of rounded sanding blocks. The blocks not only fit the various curves, they are large enough & comfortable, to fit my hand.
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A 3-1/2" Milwaukee right angle sander/grinder equipped with 24 grit discs was my "go to" device for detail forming when working with fiber glass.
It was light enough to be able to work with one hand.
Last time I bought one the Milwaukee it was about $100 and 24 grit discs were $0.60 each in lots of 30.
For heavy work, a 9" Milwaukee right angle sander/grinder with 16 grit discs was the standard.
Lew