There are already a couple threads going around about this. I don't know of any that use an aftermarket tour pak. You really have two options: king or chopped. Both from Harley and the same price. Then you can go quick detach with the 4 point docking mount or solid mount like the ultras from the factory.
Did the king tour-pak last year with detachable mounts and love it for trips. I think the chopped or razor looks better for SG though.
Ordered all from Surdyke for $1048 shipped
I went with the HD Chopped TP and detachable kit. thru Surdyke. Was not cheap!. Took about 6 weeks for paint and it is gorgeous. Come off and on in a minute.
Surdyke here too. About a grand. 4 parts - tourpack, rack, pad, lockset. Make sure to order the lockset keyed to your key code right away because it has a lead time.
I also ordered the locking 4 point rack latches, so 5 parts.
Love the extra storage and the wife loves the comfort.
King tour-pak, smooth back rest, speakers pods with stage 1 speakers and Smoked LED light bar that is running/brake/turn. I was surprised how much I actually like the look.