You can raise a Class C by putting the next size up tires on it.  We did that to gain more ground clearance everywhere on our Class C.
IMHO, the best way to increase the rear end ground clearance is to add rear air bags with the compressor control for them right on the dash .... just flip the switch to add a few more pounds pressure in the air bags to raise the rear end a bit.  Then lower the air pressure after getting onto or out of your driveway to bring the Class C back to level.
To directly address your posted question:  Research Class C motorhomes of the length that you might want .... then buy the model with the longest wheelbase for that length.  That one will have the least rear overhang - i.e. the shortest distance from the rear bumper to the rear axle.  Then AFTER you get that Class C, you can do things like increase the tire size and/or add air bags for even more clearance.
However, bear in mind that you do compromise on other issues with a long wheelbase Class C.