Hi 81,,,
I.m one of the new guys here so I can't offer any specifics as far as parts on your C-30, but I do have a bit of trailering experience.
The key points to adhere to are that the trailer stays level meaning not riding coupler high or coupler low, either one will effect handling and can become a sway hazard plus the axles and brakes of the trailer are designed to operate best with a level trailer chassis.
The other key point is that your truck should ride level while towing. Nose high and tail low will negatively effect handling, put your headlights right in the eyes of oncoming traffic, etc...
You have not mentioned what kind of trailer you are towing, is it a conventional bumper hitch or a bed mounted like a gooseneck?
You can level out the squat in your truck with airbags or overload springs, being as you are going to lower your truck I would use air bags as opposed to overload or helper springs since you will have reduced axle travel.
If your trailer is a conventional pull then I would suggest a good receiver hitch so you can utilize an adjustable ball mount. If you are pulling a gooseneck or 5th wheel setup then the trailer can be leveled by adjusting the coupler on the trailer.
All the best,
Tracey>>>>>>>>>>>>>>>>>>>