Progressive here. Went with them when we bought our MH a decade ago because Liberty Mutual didn't have an RV specific policy and was much more expensive. Progressive's RV policy covers your personal property in the MH in addition to the RV.
Since insuring the RV I've moved my auto and homeowners over to get multi policy discount. I just priced Amica for auto as my auto was renewing. Comparing apples to apples Amica was $1700+ annual to Progressives $560 (six months).