If you use your motorhome regularly, you can gauge your mileage based on previous years. If you can, it’s best to be as accurate as possible as overestimating can raise your risk profile and increase your premium.
If you’ve just bought your motorhome, consider how you’ll be using it. Take into account any day-to-day activities along with trips and holidays you have planned. You can then estimate the number of miles you might cover. If you realise you’ve undercalculated by a considerable amount, just let your insurer know and they should be able to adjust your policy.