Frost/Freeze warning tonight

Opening the faucets (or not) isn't going to make a bit of difference. The damage comes from the expansion of the water when it freezes while being strongly contained, generally between two already frozen "plugs" of water in a pipe (or in a tank that cannot deform). Opening the tap won't relieve that pressure.

A slight dip below freezing in the wee hours of the morning shouldn't be the least bit problematic. I would be very surprised if the interior of the motorhome even dropped below freezing at all.

All I can tell from your post is that your rig is likely a Class A. (Please put your rigs info in your signature). Ahhh, yes, info is in your profile.

Class A's are good without winterizing to 20F during the night. If you have the Alaska build, (dual pane windows is the tip off), then even lower. Sure, leave the faucets open. That always helps. Flush the toilet too. With the water and pump off of course. I leave the electric element for my water heater ON.

Try to choose a RV spot where the wet bays get afternoon sunshine or morning sunshine (your choice), than let the air that trickles down from the living space keep the tanks warm.

BTW, water has tons of thermal energy and it takes sustained below freezing temps to freeze it so don't worry about it too much. I keep my tanks between empty and 2/3 full during cold snaps.

With your tanks and lines empty and one frost or freeze, you'll be ok. It takes multiple days and nights of freezing weather to do any damage. We just returned from a 12 day trip and most nights, but two, was down to freezing. We had full tanks and lines and we were ok. The days warmed up to 70's and we have insulated basements.

Using low pressure air, blow the lines out.