Our 04 Allure, had a paper of weights from CC for our specific coach and sub model (High Cascade, two slides, within the Allure line.) It was mixed within the 40 lbs (
!) of documentation and manuals that came with our coach.
So, you might shift thru these and get lucky.
You sound like you are planning to get an actual weight for your coach when you can. The '4 corners' is the way to go. This is best, by paying for an actual measurement via individual scales under each position, including tag. You can also get close on the big scales, by doing full axle position weights, then running down the side of the scale with one side only. Then due the math subtracting side only from full axle. And of course, use the highest axle sides actual axle weight when looking up Tire Manufacturers Recommended PSI.
I personally look at the range on the chart, and if the weight is with the upper quarter of the scale - I bump up to the next weights line. And, I also add 5psi contingency on top of the charts recommended PSI. (Cover for different load weights over the years, long days drives in strong consistent cross winds, etc.)
Hope someone with a similar year and specific model Magna, will let you know their weights.
Suggest you update with our model length, and specific model sub name, as that might help.