Tom,
Do you have the Towmax that came on your Jayco? There are some as I understand that were recalled, not sure of the size. More info over on the Jayco forums.
As for mixing the LR E with the factory D's, Carlisle states all tires must be identical in size. But being the same load range is not specificaly mentioned, but IMO this includes the load range, as it is a spec of the tire. Because of what Carlisle states when Discount Tire mounted 3-C and 1-D on our first tt, I had them replace the D so all tires were LR C once I noticed this (maybe a month later). Tried to go the other way, but they didn't have any more D's in stock (205/75/15) at that time.
Having 7k miles to go, you may consider replacing the other tires. At least the other tire that is on the same side as the blowout tire.
Have a safe and fun trip!!!
I always run the trailer tires at max cold psi stated on the sidewall, as others have mentioned.