A Word of Caution:
Be very careful to get the right kind of tire and wheel.
For example, in the specification dbj216 posted above says: " ..... 7" X 15" truck type extra strength wheels with nylon tubeless tires (6 ply on 18 foot Caravel
and 21 foot Globetrotter .......) "
What is written is misleading.
What they should have said was: The tires were 7.00-15LT Load Range C mounted on 5.5" wheels.
At the time, a 7.00-15LT Load Range C tire had a load carrying capacity of 1520# at 45 psi. This would have been a bias ply tire.
Nowadays, a 7.00*15LT LR C has a load carrying capacity of 1710# at 50 psi (the * in the size meaning what would appear there could a "D" for diagonal (bias ply), a "B" for bias belted, or an "R" for radial.) These tires are currently available, sometimes in a Load Range D.
However, current practice for trailers is to use an ST tire and an ST205/75R15 LR C has a load carrying capacity of 1820# at 50 psi (single) on a 5.50" rim, but the tire is 3 1/2" smaller in diameter than a 7.00-15LT!
HOWEVER, none of these are available in a whitewall ! If I have this right, any 7.00-15 available in a whitewall is a PASSENGER CAR tire. You do NOT want to use those!