I don't think "power" would be the question to ask for that ride. It's not about passing people when pulling hills at 70 mph+ that you would have to worry about.
For the TransLab the more important question is how much experience do you have riding gravel two up? There would be a lot of that. If you don't have much experience on gravel solo - don't try it two up. If you have good gravel riding skills solo and good skills two up on pavement, then you may make the transition to two up gravel riding OK. If either of those skills are lacking, taking off on a 16 day trip might not lead to a blissful future for your relationship.
If you have gravel and two-up skills, don't mind taking it slower and are willing to re-spring the Glee, then you may find it enjoyable? Any bike (KTM 990, GS1200 or whatever) including the Glee is going to be a lot to handle off pavement and loaded up with camping gear and two people. It's would be up to you whether you would enjoy it or no.
I take my Wee off pavement a lot and load it up with camping gear and I really enjoy it. I know my limits and wouldn't try to take my wife and camping gear off pavement. YMMV
My Two Cents