Note I said 10" wheel, tire cross section is certainly wider, tread width can be 11" or greater potentially. (In 275/40-17, I have 11.5 cross section on 10" rim, 10.5 tread width.) What you will find as you put tires together with rim width is that tire manufs are all over the place on what rim they want with a given numerical size tire. I've seen minimum rim widths vary by up to an inch for the same size tire spec, and tread width and cross section vary quite a bit too. Things are pretty stable in 15", when you go to 17, 18, and bigger rims, they start becoming a research project.
If you must go big, go tubs by all means. Do remember tho, you will add 100s of hours to your project with that decision by the time suspension, body, paint, and tire fitment are sorted out...