I've got the factory Top box, it's small and you can't get a full face helmet to fit in. My previous box was a Kappa 46Ltr. came with a mounting plate which could be fiited to either a rack or plate. And a back rest pad was an optional extra. Key operated and could be removed leaving the plate in situ. Retailed for about £90-100. And two helmets would go in.
Theres other options and mountings at Triumph Online links on this site.
Assuming you got a 1050 theres an aux lead pick up on main loom just behind the engine towards the tank. Triumph have a
habit on wrapping the loom with blue tape at the pickup point. which you may be able to see! if viewed from nearside (left) and fiddle it down without removing the tank.Theres also the GPS pickup behind the Nose Cone. Both are permanant live, so depending what you wish to use it for you may want to add a switch into the connection.