This is just a suggestion:
has Goodyear Marathon Special Trailer tires on sale for $76.00 ea size 225/75x15 Load range 'C', Load range 'D' are $84.00ea. I hope the link works (it does!!) as searching for trailer tires is rather difficult on their site.
They ship quickly and would ship to your dealer. He won't make any profit from his house brand, but you won't be buying an unknown quality tire. I've 6 marathons on my 34' and they are working fine. I'm sure there are other trailer specific tires out there, so take a little extea time to get a proper pair of 'shoes' on your bauxite beauty!
Hope this helps,