Berkon is making ice castles frame now. They are out of Detroit Lakes, MN. You could call them and see if they would sell one behind the scenes to you. I have a Miltona frame, and the only thing that worries me is the axle strength. The crank down design is a bit behind for the time IMO. Ice castle used Miltona for a time as I understand it, and the heavier houses couldn’t handle the axle strengths and began to bow out. Ice castle for fit and finish might not be anything to brag about, but I do believe they have chased frame perfection over the years.
BTW, aluminum is great until it starts cranking because it hardly bends and then you need to find someone to fix on them.