Greetings Uncle Jack!
My '78 Minuet was equipped with Good Year Marathons from the factory (bias ply) so when I purchased new tires, I went with the current Good Year Marathon radials. My spare is the original spare that has never been used -- I purchased the coach from the original owner and he included the spare wheel and tire that he purchased with the coach in June of 1978.
Since it seems that Minuets have relatively modest weight carrying capacity, their travel weight is often very close to the GVWR. The capacity of the ST 205 75 R15 tires would be cutting it too close for comfort. My inclination would be to consider the Marathon in ST 225 75 R15 in load range C if the wheel wells have adequate clearance. This tire has 2,150 pounds capacity when inflated to maximum rated pressure.
On my 6.0 Metre Minuet, I feel that I am at the maximum that I would want to trust to the ST 205 75 R15 Load Range C tire. The loaded weight on my 6.0 Metre Minuet is usually 3,100 pounds or a bit more (3,250 GVWR).
Good luck with your investigation!
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)