I read on this fourm that most used over the road trucks will not have a proper rated front axle rating (12,000 pounds or less) or a proper brake proportioning valve for a 42 to 45 ft coach conversion. My question is, if this is true and I still want to buy a used truck what would be the cost to upgrade the axle to higher rating and fix the brake proportioning valve?

12,000 lb axle will be heavy enough if you have tandem rear axles. brakes will be set to specs. as far as i know semi's and tandem axle dump trucks have same brakes. if you go with single axle you may want to go to a 18,000 lb axle with heaver load rated tires.

12k will be heavy enough IF you keep the weight towards the rear ends. 45' coach with tandems can put you on the windshield if you step hard on the brakes! They can stop well.