We had a short queen in our first rig and we pulled the mattress out from the headboard about 6 or 7 inches and stuffed a piece of foam across it. Put a full queen size memory foam pad down over that and ahaaa !!! You could never tell the difference since your pillows went to the headboard anyway.
As far as a tub, you will only have a 6 gallon water heater and you most likely wont be able to run enough hot water to fill a tub anyway. A few couples I talked with told me that they had to heat extra water on the stove to make a decent tub of water for their baby.
