Yes, you can achieve significant improvements for around $15K with incremental upgrades rather than the full $30K air ride conversion. Focus on the highest-impact modifications first for your F53 chassis.
F53 chassis uses commercial Ford AC components. Source from Ford commercial dealers with VIN, heavy truck AC suppliers like Four Seasons heavy duty, or AC shops specializing in medium-duty trucks.
For your family of 6 with mold concerns, I'd recommend a newer gas Class A (2015+) over an older diesel pusher to minimize mold risk while still getting the space you need. The health factor outweighs the noise/comfort advantages of diesel in your situation.
Keep your RV comfortable in any weather with this AC, furnace, and heat pump troubleshooting guide.
Weak cab AC airflow with working fan and charged system indicates a blend door actuator problem, clogged cabin filter, or blocked evaporator. The blend door actuator is the most common failure on Ford V10 chassis - about 0 and 1-2 hours to replace.
Power remaining after key removal indicates failed ignition switch or stuck relay. Test for voltage on run circuit with key off. Check for hot relays in fuse box. Ignition switch replacement is straightforward if confirmed as cause.
You're absolutely right to question ISSPRO's current value proposition now that they're manufactured in India. The brand name alone doesn't justify premium pricing when the manufacturing has moved overseas and quality control may have changed.