Wall panels supporting windows

[Loamstead]

Greetings bus people.

I'm working on a 2005 International Short CE 200. Finishing up demolition now but have paused on removing the last half of my interior wall panels.

In my bus the wall panels fold under the windows then are welded/adhered to the exterior wall. I've noticed in other posts and videos a lot of buses have a metal bar between each rib that the windows sit on, but these are missing in my bus. Instead the windows sit on the plane created with the wall sheeting.

I do want to remove all the panels and am planning on using spray foam insulation in the cavities, but I'm worried that this lack of support will make the windows more prone to leaks.

Any ideas on how to add more support so the windows don't slip? If this has been covered elsewhere, I haven't been able to find it.