Damn man, that's some shit luck with the trailers. Could have been worse though. Good thing you saw the cracks now rather than later when it dumped your boat onto the hwy. I had a double ski trailer like that, that we had since 1991. One of the beams completely rusted through. Some guy still gave me $50 for it, despite me pointing out the problem. As for tires, I'll never buy anything but radials from now on. I had a 6month old tire shed 50% of the tread going 70mph. Bought it at the Tractor Supply new that season.
You're not the first to use a flat-bed trailer as a boat trailer. My buddy used to use his dirt bike trailer to launch his X4. Another guy on Jordan Lake hauls/launches his stand-ups from a van.
I think I'm gonna learn what RUSTY really is now that I'm only going to ride in salt here in S Fl. It's pretty though.
I fondly remember my early season rides in NC. They'd start about January, and we'd all be wearing full on skiing gear. It's still awesome, especially all the birds. Central NC gets huge flocks of gulls on the lakes, and it's really something to see them all take flight at once against a perfect blue sky.