My Shore lander trailer for my 96 GTX (just over 600lbs) has 12 inch tires (or as crisso says tyres).
I would stay with the larger size, they rotate less while towing.
Check the rating on the trailer for weight capacity. If it's at least 1000 lbs then you can put bigger tires on it, if there is room under the fenders
850 + gas (about 6lbs per gallon)+ misc equipment you are close to 1K lbs.