I think for bigger cabs the only solution would be a flight case and acoustic compensator (bit of wood) to tilt it back a bit.
I do this for someone else who uses an Ampeg 810 on a 2x10 combo case laid flat, and a 3x1 bit of black gaffa`d wood.
Trick then is to make sure the case isn`t that large but can fit ALL your sh*t in, like amp, cables, pedals,power etc.