That sounds like a ridiculous premium for a $75K comprehensive/collision policy on a towable, but I am in Oklahoma, you are in Iowa, two different state insurance commissions regulating rates. Also, I don't know your deductible, I set mine quite high to keep premiums down.
In storage, many companies allow you to drop collision, but I don't know who does business in Iowa. On a towable, the comprhensive will be the bulk of the premium, it is the greater risk. If you shut off comprehensive during storage, you take all the risk yourself.
Best way to lower premiums, assuming you find the right company, is to raise the deductible, shifting risk from the insurer to yourself. Even small changes can make a big difference because most of an insurers claims payments are for the smaller claims, not total loss. On $75,000, if you raise deductible from $500 to $15,000 you might see better than 50% reduction in premium. How much risk will you take on yourself?
Tom Test
Itasca Spirit 29B