With a golden, I don't see any real problems occurring. You mention house, so I assume you are not full-timing. You don't mention age of the dog, so I'm assuming you'll be adopting an adult dog. With that, here are my suggestions.
Before you get the dog, move objects that are on high places to safer places. Cats will normally seek high places where they can see what's happening, but not be in danger (siamese especially). Let them have that security against a creature so much bigger.
When you get the dog, bring it in on a leash and keep the leash on while you let the cats check it out. Let the cats approach on their own - don't try to walk the dog to the cat, or bring the cat to the dog. If your cats are curious siamese mixes, they won't take long to start checking out the dog - let them. Don't interfere, other than to keep the dog calm and to talk encouragingly to all. Most dogs learn with one swipe of the claws that the cats are in charge - how quickly your cats will do so, is dependent upon the cats. You may want to trim the cats' claws in anticipation to reduce potential damage.
If you're able, sit on the floor with the dog, petting it, while you talk to the cats. If you cant get on the floor, sit in as low a stool/chair as possible. This shows the cats that the dog isn't a threat. Keep doing this each day.
If the dog is a chaser, keep it on a leash whenever the cats are around. Since you want them to be able to live together in the RV, getting them used to being in close quarters without chasing, etc. is important. You want to ensure all 3 are safe with each other without having to crate or lock anyone up.
To get them used to sleeping around each other, I use a tie out cable and wrap it around the headboard or leg of the bed. At night, I attach the other end to the dog's collar. I leave enough room for the dog to lay down in the corner with enough slack so that the dog can be completely on the floor (in case it falls off the bed during the night). The cats just roam as they wish. The tie out keeps the dog from chasing the cats during the night. As they get accustomed to remaining on the bed throughout the night, I add more slack to the tie out. If they try to chase a cat, the tie out slack is reduced back to the start. Once the tie out is at full length and there are no chasing attempts, I stop using it. The dog is now trained to stay on the bed throughout the night and not worry about the cats' nocturnal wanderings. If you don't want the dog sleeping on the bed, then adjust the above in a location where you can place a dog bed. The benefit of the bed is that you are more likely to wake if the dog suddenly decides to wander (or chase) during the night.
I have done the above for years while fostering. When someone brought over a new foster dog, they would be amazed when the cats would suddenly appear in the room, relax on the chair arms, etc. and quietly study the dog waiting for an opportunity to correct bad behavior. :)