Good Morning! I searched for this topic and found this thread. I had a similar case, but not well damage from a blow out; simply holes worn through the undercarriage "tarp" material from all four tires rubbing against it. I can't believe they don't protect that area somehow! Maybe they do more now, my TT is 6 yrs old.
There isn't much room for tire travel, it doesn't take much of a dip or rough terrain for the tires to touch the undercarriage.
Two months ago we got our first camper, an 06 Wildwood, with holes and exposed insulation above the tires, so I temporarily patched them with duct tape to prevent more damage. Well, I just finished the more permanent fix suggested in this thread and covered the underside with sheet metal, stainless screws and undercoating. Here's a few pics...
Started with 2 pcs of duct metal. Slide side needed trimmed a bit - other side, simply flattened the duct, was the perfect size:
And the slide side:
Then sprayed both with undercoating.