Tom, here's
another outfit I've used that has a good selection of parts.
One thing you might consider that might add a bit of life to the springs is spraying them with some LPS3 to penetrate between the leaves and then spray them with automotive undercoating before you install them. I did that to my 1985 EZ Loader roller trailer and I'm still running the original springs! I have inadvertantly dunked the springs a couple of times, although I don't normally have to dunk it. I've also repeated the LPS3 spray a couple of times.
BTW I emailed you a list I came up with of the weights of typical boat gear that might give you some idea of total boat weight.
Denny