Here in TX you have to change the zoning to change the tax rate. You should also be careful changing the zoning to MHP as it may impose city code requirements you do not have today.
I would also consider fighting the taxes in general. This may not apply to you, but I have seen cases where a county will value the Park based on what someone paid for it - instead of the unimproved land value + the aged infrastructure. The argument to the tax office is that the land was purchased based on the business value, not the land value, which includes having lots of tenants with their own homes paying lot rent. If those tenants decided to leave the next day then the business value would be zero, but the land value would not be zero.