After the very first night we spent in our RV - our dogs understood that it was a "house". When they were younger, Ike and Jack would get taken on long walks before we'd leave them, with shades drawn and the TV on for background "noise" (just like we do at home). The longest we left them was 7-1/2 hours while we took a sightseeing cruise in Alaska (after walking the perimeter of downtown Valdez) - they were STILL passed out when we got back :-)
And if you can, just take "baby steps". Leave your dog for just a short while (maybe just stand outside the RV for 5 minutes listening for sounds) - then increase the time gone. As others have said - most dogs who are fine at home are fine in an RV.