Is my income from motorhome and caravan rental taxable?

It depends on the country in which your vehicle is registered. 

Sweden
The rental income you receive as a vehicle owner is taxable capital income. It is important to note that you can deduct the tax when it comes to costs associated with the rental. For motorhomes, the Swedish Tax Agency has today established a deduction for wear and tear of SEK 9 for every 10 kilometers, unless a higher cost can be demonstrated.
There are also deductions for supplementary insurance and other additional costs that have to do with the rental. These do not apply to a standard motorhome insurance, cleaning, taxes, service, parking space etc.
You can calculate the tax by calculating your rental income minus valid deductions, and then calculate the tax on the surplus, which today is 30%. If you have thoughts about renting motorhomes and caravans and taxes, we recommend that you read more at the following link from the Swedish Tax Agency's website.
Swedish Tax Agency's web page about renting out resources
If you run a business and are liable for VAT, you need to issue a receipt to the customer for the amount you have earned and specify VAT there.

Switzerland

We recommend that you declare your rental income to the tax authorities. For more information on taxes (which deductions can be claimed and what you have to pay tax on), we recommend that you contact your financial advisor or the tax authorities. You can find your rental income in your MyCamper account under "economy" and then you'll find your payouts. Together with our advisor, we have created an information sheet about the tax consequences of renting your vehicle via MyCamper.