Owners can choose whether to allow pets in the RV. On the listing you will be able to see whether an RV is “pet friendly” or not. Additionally, in the search you can filter the results to only include ones that allow pets.
If you have pet allergies you should make sure to ask the owner if pets have been in the RV.
Bear in mind that some owners have severe allergies, and if the RV does not allow pets you should make sure not to bring or let any pets in it. If pets were brought into an RV that is not pet friendly then the owner can impose a fee for this violation.
If a renter shows up with a pet to collect an RV that has a “no pets allowed” rule, the owner can refuse to release the RV and this will be considered as a last minute renter cancellation.