As I don't see a dedicated "Reverse Trike forum, this is as good a place as any to post.
I would think for mileage, you might want to look into a car tire for the rear. A buddy of mine put a car tire on his 2 wheel Gold Wing and he loves it and gets like 50k out of it.
I just don't like being behind him, when he leans, most of the wheel tread is off the ground. Really freaks me out. On a Reverse Trike, I would think that wouldn't be a problem.
Hopefully the Reverse Trike owners will chime in soon.