Sorry it is not a lot of use to you, but I worked in the industry for over 40 years for three different companies. Quite simply like everything else we buy the cheapest is the cheapest for a reason, and that is usually because it is inferior, but I do accept there is the odd bargain out there, but unless you know the business you cannot be sure.
With car insurance there can be bargains because the rates are increased with results and inflation at different times by different companies, so if you can get a policy before the rates go up you can do well. Generally caravan policies are simply a percentage of the sum insured, although the area you store it can also be used by some companies, so the about to raise the premium point does not arise. With car insurance the liability risk is the premium driver as that is where the huge claims are, this is partly independent of the car model, but not entirely.
The best policies have a DEFAQTO five star rating, if they do not have this then something is missing and may be more. If it does not have the rating then I would not touch it. I accept you only know how good the policy is when you have a claim, but if the adverts emphasise cheap, that tends to be what they are, rather than good.