Hi Andrea, it's kinda hard to answer your question exactly because
we don't know what your dealer did when they winterized.
1st open the outside hatch on your water heater and see if the
drain plug is screwed onto the bottom front of the tank.
It should be tight. If the plug is laying in there you'll need to
wrap some teflon tape on the threads or use pipe dope on the
threads and re-install the drain plug.
Some folks find that if they have a "4 way" lug wrench one of
the arms on the 4 way will fit the drain plug.
Don't over tighten it but it needs to be snug.
Now open what ever you need to open to see the back side of the
water heater. On my trailer I open the outside storage hatch which
is right next to the outside water heater cover.
There might be a plywood paned that partially or mostly blocks your
view. On the back side of the water heater there are probably
2 black valves. Mine are hard to reach, I have to half way crawl into
the storage area or I can pull out 2 screws on that flimsy plywood
that's in the way and remove it. With the plywood removed the
2 valves are easy to see.
Each valve needs to be turned 1/4 turn.
One is "sideways" and needs to be turned so the handle is up and down.
One is already up and down and needs to be turned sideways!
Your fresh water tank has a drain valve. Mine is accessed by going to
the other side of the trailer and opening the other outside storage
hatch. My drain has a little tiny T handle on it. If the handle is pulled
up-- the drain is open. If your handle is up just push it back down
to close the drain. If you don't want to use the fresh water tank
you can leave the drain open.
Connect a garden hose/RV white or yellow drinking water hose
to the outside garden hose connection on the trailer and the other
end to a city water spigot. You probably should have an RV garden
hose pressure regulator on one end of the garden hose too.
Turn on the city water valve at your house.
Go in the trailer and open a hot water faucet.
You might want to drape a hand towel over the faucet as it will likely
run pink and then start spitting air. After a minute or 2 of air the water
heater will be filled and you should get water again. When it runs clear
shut off that faucet. Now you can flush all the other hot and
cold faucets to get the pink antifreeze out.
Now go outside to the outside water heater hatch.
Near the top of the water heater tank is a little pop off valve.
It has a metal tag on it and a little lever.
Pull the lever and you should get water out.
That proves the water heater is full of water and safe to light.
You might want to read this thread
new water tank taste
as it pretty well covers how to sanitize a new water system.
Once you get water pressure everywhere and the air and pink antifreeze
rinsed out it would be a good idea to look under
all sinks and around all fittings on the back of the water heater
and fresh tank to see if you can see or feel any drips.
I've had 3 trailers over the years and every one had a leak somewhere.
Maybe you'll be lucky but you should check as many places as you can.
Good luck and happy camping!!