Originally Posted by JohnnyK81
...but I still think I'll need something longer for the roof, and possibly quarters of my fastback.
Not only longer sanding blocks...but I found longer "spreader tools" are helpful as well. And plexiglass isn't a bad way to go.
Here is a plexiglass "bondo applicator" that I used on my sedan/delivery:
And this applicator is simply a piece of roof flashing (you have to cut a very straight edge on it or use the pre-cut edge at all times). Gets the filler spread thin and even over some pretty difficult curved areas.
And here is my long plexiglass block sander. The "handles" are 35mm film canisters epoxied to the back side of the block. And the sandpaper is stick-on type.
And here it is in use.
Although I didn't try it, I've also heard of folks using aluminum 4' "yard sticks" such as the one shown here. These would bend nicely to conform to any slight crown in the metal while remaining flat over a very large surface area.
Holding on to them might be the biggest challenge.