Thor Avanti renovation is very doable. Jackknife sofa can replace dinette, vinyl plank flooring is popular, and mattress can be replaced with standard size in most cases.
Class A offers more space and amenities at 28-33ft. Class C easier to drive with better MPG. For your needs (king bed, large shower, recliners, tow SUV), Class A likely better fit. Test drive both before deciding.
Your RV sewer hose will likely freeze at 25°F, especially with the uphill section that creates standing water. The two-inch rise at your hookup point is particularly vulnerable to freezing.
To fix parasitic power draw through your 2006 Damon Challenger's instrument cluster, use a multimeter to isolate the circuit, check common culprits like clock memory and sensor wiring, and find alternative wiring diagrams through Freightliner chassis documentation or aftermarket sources.
RV propane detectors should be tested monthly using the test button, replaced every 5-7 years, and positioned correctly near the floor. For alternative testing, use a small butane lighter held 6 inches away without igniting it.
Running generator while sleeping can be safe with working CO detector and proper precautions. Close exhaust-side windows, check wind direction, and ensure CO detector functions. Many RVers do this safely.