Ouch, stab me in the heart!!!
You are right that Crowns were not common in rust belt states. However, another California bus builder was Gillig. Most, but not all, of their buses were built using steel instead of the aluminum skins like Crowns. Also, like Crowns they were primarily West Coast distributors of their buses. I have been told by Gillig enthusiasts that old Gilligs are hard to find as so many of them rusted out. Don't know if that is true, but that is what I have heard from these Gillig experts.
Logic tells you that in rust belt environments, high quality aluminum is better than steel. Logically, thick and high quality marine grade plywood that does not rust and resists water penetration for floors is better than a steel floor that will rust. Crowns were also made with heavier grade steel beams and frames than other buses. In short, it was a better made bus. You paid for that better quality build as a Crown cost about 40% more than a Blue Bird or Thomas when they competed head to head. When I was a senior executive in a large school district I remember arguing with the Superintendent about having the District buy Crowns vs Blue Birds. All he saw was the initial upfront cost. As a business guy, I saw the useful life stats and the cost per active year of use, and it was Crown hands down. When you factored in the life expectancy of a Crown vs other buses, a Crown was actually cheaper over its lifetime by a substantial amount. Plus, they had a bumper to bumper 20 year guarantees, much better than any other bus ever made.
I absolutely agree with you that Crowns are a pain to convert. The giant twinkie appearance looks cool in an old retro kind of way (right out of the 40's). However, it makes conversions much more difficult.
I can't speak about your issues with Prevost owners. Never had any as friends. I believe that all of us have a right to be passionate about whatever bus we decide to convert. Blue Birds and Thomas buses, properly maintained, are great buses and make great conversions. Given the straighter lines of these buses, they also make a far easier conversion.
Any platform will work if its bones are good. I have seen too many posts where skoolies are having to spend massive amount of time fixing their rust issues. I will take the pain in the ass problems of rounded roofs and corners anytime over the problems of rust.