For trolling I use a full spool on every reel, I only use monofilament now for trolling, but even when I used super line, same deal. The nice part about using full spools with the super line was I could then transfer it to my casting reels... the stuff ain't cheap.

For the casting reels, the amount of backing I use depends on the amount of line available,  I have some reels with full spools, some with three-quarter, and some with half, I just keep spinning the line around until it's basically used up. Obviously you have to use a little bit of mono backing with any superline to keep it from slipping on the spool with a "full spool".

The best way I have found for spooling fresh line is to put a dowel rod through the spool and hold that in your stocking feet on either side with your toes on so you can increase or decrease pressure as needed. When you do this be aware that whatever the spool will setting on could be damaged from the friction. On my casting reels I always tie it off in the yard,  then re-spool it real tight, better casting and less backlashes. If you decide to empty the reel and re-spool tight, you'll need to over fill the reel slightly because everything compresses. 

Flipping it around like that with the backing is very clever... I just learned something!  I admit to coming up short more than once on the same reel when reversing the line.