Many compact electric heaters have different settings that use different wattages. a 1500watt heater is designed for typical 15 amp, circuits, which is what your trailer has. Just be aware that unlike a home, it's likely all or many of the outlets in your trailer are on a single shared circuit (except the microwave which is in it's own circuit as is air conditioners). Running a heater on high and using a hair dryer might trip a breaker. You can get an idea of how many separate circuits you have by checking the breaker panel. No need to spend extra on a heater specifically designed for RVs or marine use. Just look at the box, to see if it has low medium and high wattages and has the features that work for you - remote, thermostat control, etc. We've used a compact DREO model 316 brand heater that doesn't take up much space, is quiet, has a thermostat and three heat levels - 1000, 1300, and 1500watts. We originally used it as a bathroom heater in our Class A, but now use it in our 2018TB.
One thing to note is most modern RVs use a branch off the propane furnace to run heat into the wet bay. It's the case with our 2108TB, especially if it's advertised as being all season or in the case of our 2108TB having the Comfort package. As is mentioned above, it takes quite low extended temperatures to freeze plumbing. In these trailers the lines commonly run though the interior of the of the trailer so are a little less prone to freezing. In the case of our trailer, domestic water enters through the wall in the same cabinet as the hot water heater runs along the base of the inside bathroom wall, under the shower and into the kitchen. The holding tanks are in the belly, but one trick is to be sure to try to keep your fresh water tank full as it behaves like a thermal mass, that takes extended time in low temps to get cold. In shoulder weather, we fill the tank, use city water when daytime temps are mild, and disconnect and drain the hose at night. Some use heated RV hoses. Where running the furnace or somehow providing supplemental heat to a wet bay is required is when temps never go above freezing even during the day - flat out winter camping. The lowest temps we've camped in was 7F at night, and 14F during the day. It wasn't our choice to camp in such temps, a winter cold front caught us on the road one week. Fortunately it was in a Class A with easy access to the wet bay where I ran a small electric heater, not so easy in these trailers.
Another cold weather trick is to open the cabinet doors under the bathroom and kitchen sinks. Doesn't need to be wide open, just propped open an inch with something like a folded towel.
A quick search showed me that your trailer has heated tanks. If you are still concerned with overnight temps, you can always switch on the tank heaters. Just make sure your tanks have some water in them. For us, we've never used our tank heaters so far when camping in the shoulder season when daytime temps are mild, and nighttime temps hover around freezing. Hope some of this helps. Sounds like you have a great trip planned.
