The extra torque is well-absorbed by the frame and stabbers. We don't notice any more movement than with the single-step.
And of course the double's don't match up underneath like the single's do. They must plan this stuff ahead of time! To mount my new double, I made mounting brackets from the sides of the single. If you want to do that, look at the long channel used by the single step to glide in and out. Hacksaw the 'meat' off each end of the channel and presto, instant mounting brackets are in your hand for the double. A welder charged me $50 to weld the brackets to the double, even painted 'em for me.
Camping in the Pacific NW
2014 Flagstaff MAC 206st