[Only Toyota for me]

I had goodyear marathon C rated tires on my 4k lb 1999 boat, and they started weather cracking last year. Puts the tires at 9 years old, according to boat manufacturer date ONLY. Not the date the tires were made, which could be up to a year older. The boat was stored in our heated garage virtually the whole time as well.

If i was in your situation, i would get rid of them and go with a D rated tire if you can find one. I wouldn't even chance it if i were you. A blown tire can cause thousands of dollars in damage.

Them marathons don't have a good track record either.