True North wrote:
I'd get rid of that old trailer and buy a spanking new galvanized model
that is a proper fit. Those rigs must be cheap down there. Even up here a
light trailer is just over a grand.

On Mon, 18 Mar 2019, Bill wrote:
It may be a trailer in great shape. Just bought with the small tires that
do not do well for long fast trips.

I think you're both right. The trailer is old but it's galvanized, has
new bearings, and in great shape, except it would need new tires even
if I stuck with the 8" rims. You can't have too many trailers though.
In fact, right now I have more boats than trailers. So another one
might make sense too. Especially if I spend much more time fiddling
with this wheel size/spacing conundrum.
........

Have you checked with Walmart? They have rim including tire that will fit about any small trailer. You might look them over. They have at least two rim sizes that fit a standard 4 bolt pattern, and various std 5 bolsters.