When we picked up Blue, Reace said to keep the tires at 45 for the best ride. The Goodyear 15s are weight rated quite a bit higher than a 17 is likely to see, so I have been comfortable with that. Usually I keep them at 47-48.
All this talk of tires reminded me that I want to coat the inside of the tire well with some truck bed coating. One major danger from a flat with fiberglass trailers seems to be potential damage there. After watching the "Mythbusters" episode about bed liner I believe it would really help prevent major damage from a shredded tire. I found that Rust-Oleum makes it in a spray can and gets excellent ratings on Amazon, so I picked up a can. I'll try it soon and let you know if one can is enough to do both sides. I am hoping that it will stick well to fiberglass.
Eric (and Mary who is in no way responsible for anything stupid I post)