Hello USCGGM...
The 31" tires are great. The trailer is sitting at stock ride height too, thought I might need to do a SOA? There is tons of room (vertical travel) and no rubbing worries. I loaded it yesterday with 550 ish pounds and it didn't really touch the ride height. Handled great, pulled smooth.
The wheels are 15 x 7" with a 3.75" backspacing. They are from JC Whitney, great deal $52.00 each, free shipping to Canada, no duty or taxes. I would prefer a 4.25 inch BS, but they didn't stock that size...and these match the wheels on my XJ so yeah. I really like the look, and the wider stance makes me more confident that it will not flop over as easily.
Looking forward to modding this trailer!