Hey SenecaDave,
I went to college in Elmira and I did my Scuba Cert in Seneca lake in December, LOL! Anyway, lots of good advice already posted above. I think you will be fine. If your trailer is rated at 10K pounds (that is on the ID plate right?), then you must have 5K axles and springs. Most boat trailers I see for lighter boats (under 7K) use a pair of 3.5K axles, 7K total. An easy way to tell is if you have 6 lug wheels/hubs vs 5 lug. looking at the pic, although hard to tell without zooming, it does appear you have 6 lugs. Even if it turns out that you don't have the heavy axles I highly doubt your Ericson 25 is even close to that heavy, Sailboat Data has it at 5100. With the boat plus cradle plus any extra gear you'd be perfect with a set of 3500 pound axles and springs.
For securing the cradle to the trailer, just drill some 1/2" holes through the cradle frame and use 1/2" galvanized bolts and fender washers. Make sure you are securing to a cross member or main frame rail of the trailer frame and not just through the deck planks!