I think you should forget about a medium duty. Go HDT (heavy duty truck). It's actually likely cheaper to buy one than an mdt. Look for an hdt with a large sleeper and you're set. There are companies that build nice big living quarter type sleepers. Used to see them being used by the moving companies.
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'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio