Five inches probably won't be an issue. I doubt that ten would be an issue. There are many RV's, still in good condition, that get snow accumulations in excess of that and survive.
Where there could be an issue is ice / water intrusion around fittings such as the air conditioner gaskets. Snow can cause an ice-dam to form, and from there water could have nowhere to go but into gaskets. For this reason, I really think that the well-cared-for RV needs to be under a good quality cover in the winter. ...either that, or the owner has to monitor the snow/ice situation carefully, and plan on replacing gaskets, caulking, etc., more often than if it were covered.