Someone was just discussed this propane rubber hose issue a few days ago. Some use a rubber hose with grommets to reduce chafing of the hose from where it passes through the floor. Others prefer a standard residential hardline under the floor to several ports inside the bus through the floor.
Small propane heaters and camp stoves have small pressure regulators on each appliance. That means you have to bringing a high pressure line inside the bus with you probably leading to a manifold to feed several appliances.
Permanent propane appliances won't have those small regulators on them and would need the regulator to be mounted outside to support the low pressure side of the system. Consider that RVs have the pressure regulator on the tank outside, and only low pressure lines go inside the living area.
Obviously be very careful using a rubber hose as a high pressure line inside your bus. Sorry for being long winded, but I've had accidents with propane.