Before you buy tires, get it weighed.
You will probably want load range D, but you might need E for one end or the other. It also might be that D&E are the same price.
And NO, stay with one tire size. That way you can carry a spare and rotate tires even if the LRE are too heavy for one end.
A lifelong waterman and his bride going dry places for as long as the fuel money lasts.