Ok... I got my handbook in the mail today and I've found two pertinent sections.
#1 On page 4 under "Definitions", a "Commercial vehicle" according to MVC 257.7 can be a vehicle "... constructed or used for transportation of goods, wares or merchandise...". That's pretty broad, but would include a Deuce (as well as every pickup truck ever made). The very next definition is for a "Commercial motor vehicle (CMV)" according to FMCSR 390.5 specifically states that the vehicle must be "... used on a highway in interstate or intrastate commerce to transport passengers or property...". To me, this excludes any vehicle not used for commerce.
#2 On page 7 under Getting and Displaying a DOT Number", it states "A Michigan motor carrier operating commercial motor vehicle/s
in interstate or intrastate commerce must apply for and obtain a USDOT number." And a "Motor carrier", as per page 6, is defined as "Any person or entity that operates commercial motor vehicles to transport cargo or passengers..." and the definition is simplified as "Anyone operating a vehicle meeting the definition of a 'commercial motor vehicle' to support any type of business activity or service..."
So... my conclusion is that a privately owned deuce used for recreational purposes does not meet the definition of a "Commercial Motor Vehicle" because it is not being used for commerce. The same reasoning applies to getting a USDOT number. If it's not a CMV, then it's not being used for commerce and does not require a USDOT number.
And further research into Michigan laws has found this: MCL 207.1002 (Motor Fuel Tax Act), section 1(i) “Qualified commercial motor vehicle”, subject to subdivision (j), means a motor vehicle used, designed, or maintained for transportation of persons or property and 1 of the following:
(i) Having 3 or more axles regardless of weight.
This would seem to include a deuce except that subdivision (j) states: “Qualified commercial motor vehicle” shall not include a recreational vehicle...
Also,
MCL 257.7a specifically states: A commercial motor vehicle
does not include a vehicle used exclusively to transport personal possessions or family members for nonbusiness purposes.
To me, that last part says it all. No DOT numbers for me. Whoever got nailed in their pickup truck hauling a trailer got royally boned.