If you're going to recover it, then depending on how much effort (or differential effort) you'd be willing to tolerate, you might consider taking an approach like what's used to build "stitch and glue" boats (kayaks, canoes, and other small boats). This involves using fiberglass fabric applied to the surface and seams, then sanded and painted. One advantage of this is that you'd end up with what's pretty close to a light but fully protective and almost indestructable case. Using this technique, you can build an extraordinarily strong 16' kayak that weighs only about 35 lbs, for example.
Gluing any kind of fabric on is messy and very difficult to avoid wrinkles and get the edges/seams right. With the fiberglass (liquid + fabric), you get a hard surface where you can sand out any imperfections. I think you can get all you need at Lowes or Home Depot or auto stores. You wouldn't really need to try to use sheets of the fabric on the larger surfaces, but just use strips butted together and filled with the liquid fiberglass. It would be probably be more expensive than any kind of standard fabric glue-on approach, but you'd end up with a case for the ages.
Just a thought.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)