I haven't sanded under my hood (or trunk) yet... but if time and energy allows I will.
I have a young family which kind of changes the priorities a little (in a good way),
so I'm unlikely too. I would like to think I will get around to it eventually. Who knows?
FWIW - I've been using Abralon & 3m products to sand.
Starting at 120grit and doubling it every turn.
ie: 120 - 240 - 500 - 1000 - 2000 - 4000 to polish
I've found the Abralon stuff is quite good.
The tricky bits are the smaller nooks and crannies I find the most time consuming, but seeing the end result, the reward is therapeutic.