The subject says "7k car hauler". That's two 3500lb axles, which usually means 15" wheels, and either 215 or 225 size tires.
My experience is this: Bias ply trailer tires are durable and great for short hauls around town. However, they are VERY picky about alignment, and I've had them wear quickly (less than 5000mi) on a single axle boat trailer that didn't wear radial tires at all. For longer runs like the OP is suggesting, and especially for a two axle trailer, I'd recommend sticking with radials for best wear.
I am done with TL (trailer use only) tires for any trailer I plan to keep and use. They are generally made as cheaply as possible no matter what brand you buy, and unless you use Load Range D or E 15" trailer tires, they are NOT better in any way than normal (P-rated) tires. Even going with a name brand trailer tires (Goodyear, Marathon) has not worked out well for my friends and I.
We now use P215 or P225/75R15 tires on all of our car and boat trailers, and LT rated tires on heavier trailers with 16" wheels. The exception is one set of Goodyear G614's that I have on my Gooseneck. The G614's are Load Range G, and I bought them with low miles off CL for $100 each. They are over $300 each new, and are really heavy tires that wear like iron and hold up GREAT, particularly when used well under capacity in lieu of a LR E tire. (Not helpful to OP, but perhaps to others...)
We've experienced no tire failure problems with the non-trailer rated tires, even on tires that are 10+ years old. In my experience, and by most mfg's recommendation, trailer tires that are 5 years old should be replaced. They may be fine for around town, but I certainly wouldn't take them on a longer trip... The last set of P-rated tires we had on the car hauler were P215/75R15 Goodyear RT/S's that were bought off CL as a take-off set of wheels and tires from a new (at the time) Jeep Wrangler. (~2000MY) They lasted 15 years before weather checking and wear prompted their replacement about two years ago. We replaced them with P225/75R15 Cooper Discoverer H/T's. No issues so far.
