When I planed the lumber for my hardwood flooring, I used a cheap Delta lunchbox planer and man did I ever beat on it. 10 inch wide Ash,air dried for 3 years and 14 feet long. I could not believe it took the pounding I gave it.
The one thing I did though was make a bed for it. I used 2x6's 16 feet long, and cut them so that when the planer sat down in the notch in the middle of the boards. I measured carefully and used plywood over the top of the 2 x 6's. This gave me a 8 foot table roughly on each side of the planer. I put a layer of that aluminum trim that comes in rolls over the plywood for slipperiness and put the whole thing on sawhorses.
I still had to drive some of that Ash through the planer as the rolls would not pick it up. You will have to do the same thing with 6 x 6's, but that should still give you a good finish.
I have no intention of traveling from birth to the grave in a manicured and well preserved body; but rather I will skid in sideways, totally beat up, completely worn out, utterly exhausted and jump off my tractor and loudly yell, "Wow, this is what it took to feed a nation!"