(2) "Motor vehicles" not required to be registered for use on public roads or property which are: (a) Used solely to service a residence; or (b) Designed to assist the handicapped;
And under the liability coverages the exception is as follows:

a. In dead storage on an "insured location";
b. Used solely to service a residence;
c. A riding lawn mower that, at the time of the "occurrence", is being used to mow a lawn;
d. Designed to assist the handicapped and, at the time of an "occurrence", it is:

(1) Being used to assist a handicapped person; or
(2) Parked on an "insured location";

e. Designed for recreational use off public roads and:

(1) Not owned by an "insured"; or
(2) Owned by an "insured" provided the "occurrence" takes place:

(a) On an "insured location" as defined in Definition B.10.a., b., d., e. or h.; or
(b) Off an "insured location" and the "motor vehicle" is:

(i) Designed as a toy vehicle for use by children under seven years of age;
(ii) Powered by one or more batteries; and
(iii) Not built or modified after manufacture to exceed a speed of five miles per hour on level ground;

If the tractor fits these parameters, or those on your form, then coverage would apply. Otherwise, we know of no endorsements that would provide coverage for a large tractor. The inland marine PM 00 32 Motorized Ground Maintenance Vehicles form might work, but it would depend on the details.
--