This is what I've used on my 8,000-lb GVWR Silver Streak, tandem-axle:
Yokohama RY215 LT Load Range D, 15", 8-ply rating in 7.00 x 15 (7R-15):
Currently Available Prices and Sizes
They balanced well (less than 24-ozs per wheel/tire assembly) and exactly meet the load rating recommendation by the trailer manufacturer.
Despite the description given on the website above these are LT tires used for commercial vehicles. I run mine at the rated 65-psi.
The corporate site has a good description and picture plus specs:
1990 35' Silver Streak Sterling
; 9k GVWR.
2004 DODGE Cummins 305/555; 6-manual; 9k GVWR.
Hensley Arrow. 10-cpm solo, 18-cpm towing
Sold: Silver Streak Model 3411