There have been some good comments so far.
As mentioned a tankless system can only impact so much change or delta in the temp based on flow. The heating unit is only so big, (45,000 BTU) and the heat exchanger only so long so as the water flows through it the higher your flow the less time it spends in the heat exchanger and the less the temp will rise.
So as temps drop on your inlet water (cold side) you will need to slow down the flow as much as you can. Some options for this are to turn down the hot and the cold off. This can be difficult with a single handle control on a shower. I wonder why they install that type of control in an RV with a tankless system? Since you can't really control flow with the valve, you can add a more restrictive shower head. In the shower that is about all you can do.
In looking into these systems a bit more I discovered another feature that might be on your water heater which may help out a lot. I mentioned it briefly here:
http://www.jaycoowners.com/forums/f6...tml#post509555
If you go to that post I have a link to the manual found on some of the Jaycos. It mentioned on page 14 that there is a flow control valve on the water heater. Now this is the manufacturer's manual and it sounds like it might be an optional feature. So open your water heater panel and see if you have that knob. If you can, turn down the flow rate here and it will slow the water passing through the heat exchanger and increase the delta on the hot side. When you have colder city water or the tank water is cold, this will impact more change and get you hotter water. As you get into summer you can open this valve up more as you won't have as hard of a time hitting the temps you want. Another thing you can do is if you have the cold weather package which has a tank heater on the FW tank, you could pull water from that as someone mentioned and have your tank heater on to bump up that inlet temp a bit. Not sure how effective that method is but another thing that might help.
I have mentioned before in other threads that we have one in our house and I love it once we figured out some minor differences in how to use it. However we are not moving it all around the country because how high you are above sea level will impact it and your water inlet temps will fluctuate a lot. Where those things are constant not to mention my 199,000 BTU unit can impact more delta on the water temp at much higher flow rates than the camper units can.