Hmmm never attempted to get the doubles on an airline, pony yes. That said I am sure it could be done if you had the $$ as you would surely be overweight.
My travel rig is a BP/W, 30lb lift Mark V, 6lb stainless with a 6 lb STA and pockets mounted, inverted at the lower edge of the plate for weights as needed. With a 3mm wet suit in salt water w/AL80 I need about 4lb in those pockets. Packing all my gear including that in a roller bag I still have room for other important things like normal clothing and a towel or two and remain underweight. I have used this in many of the sites I travel to and it is a pleasure to dive.
I do not know if too many places that rent doubles. By special request we will.
Hope this helps
Best fishes!!!