I replaced my fuse panel at the same time I replaced my converter. I purchased a fuse panel from Vintage Trailer Supply for about $40.
I found the job harder than I imagined. 12v
wires in our trailers are rather large in diameter and stiff. They carry quite a bit of amperage since there is only 12volts "pushing" the electricity through the trailer. The big, stiff wires were difficult to thread through the small, rather flimsy fuse panel. Maybe this fuse panel was meant for little automotive wires, not big, burly Airstream wires. The Airstream original fuse panel was much larger and more robust.
I'm worried when you say you have wires are brittle. Maybe you mean stiff? I did not have brittle wires or cracking insulation on my 66 Trade Wind. A new fuse panel won't fix your wires. I think you better get an RV electrician's assessment of the wiring. We don't want you to go up in smoke!