You aren't over thinking...it pays to know and be prepared.
I agree that to say "if the basement is heated...you'll be ok" is indeed a "well maybe" statement. If the temps drop into the teens and will stay there going down the road the cold air can and will infiltrate the basement areas and cool it down. Ok is relative to how warm the furnace is able to heat the lower bays. The only way you will know is to try it.
I fully agree, install a remote temp sensor in your utility bay to monitor the temp. If indeed you find the temp near your lines and pump is at, near, or below freezing you may have problems. At that point you can turn up the furnace so it runs more, put in a 60 W bulb when you are parked, or winterize.
In fact I'd try it out before you leave, setting the heat to run in the range you would use then monitor the temp. Only then will you know how warm you are able to keep the water areas.
Usually, if the fresh, gray & black tank are no more than about 1/2 full they will not be damaged if they freeze a bit but I don't think they would freeze solid unless in deep cold long term.
I'd monitor the weather before you are about to leave and make the decision whether it will be wise to winterize before you leave.
It's not fun to travel winterized but it is entirely doable if the trip down & back won't be more than a few days. You can still use and flush the toilet if the tank if nearly empty and add enough "pink stuff" to help prevent freezing solid.
Good luck
