I love my MarkBass gear and was quite happy when I switched from Ampeg. I have not regretted the decision for a second. I do get why some people might not like their cabinets though, they have a noticeable low mid bump, so I am not as quick to recommend them.
OP is it possible for you to rent a MarkBass rig? I would do that to see if it works for you, in your band before I went out and bought anything. I would also look at other brands, if weight is the only prerequisite then lots of brands can fit the bill here. I would personally recommend Epifani but that is based on my tastes.
You could always get two cases. I am assuming you are doing major touring to necessitate those road cases, I do not go that far, so for me I would ditching the cases all together. I can carry my bass, pedalboard, amp, and cabinet all in one trip if I really want to, so adding a case like that would just slow me down.
Carvin LB76 / Dingwall ABZ ! Support Local !
MarkBass SD 800
Epifani UL2-310 / fEARful 1212/6
! Rocking against all gods !