The 'wear and tear' from flat towing would be primarily additional miles on tires and brakes... I keep track of towed mileage myself (rounded to thousands) just to be aware.)
Cars without a 4WD transfer case (and I would think more so automatics) - may accumulate 'mileage' to transmission fluid changes...
I would NOT expect to see miles reflected on the odometer of any current vehicle... The ignition is typically OFF.
Dolly tow takes any wear away from transmission/front tires - but still accumulates mileage on rear tires (again not reflected on odometer)
Trailer eliminates all wear on vehicle - but adds the need to register, store (home and campsite) and maintain...
Some limits on what you can tow based on tongue weight (10-15% of tailer weight should be on tongue).
Could argue it 'adds' wear to the MH from the heavier tow... but not sure how to quantify...
Not knowing what coach you have - but would guess the RV costs 2-4 times more than the Focus??
Pick your poison...