which brands have good winter packages?

At least here in this part of the northeast, there are not many campgrounds that are open for the winter. I think were are at total of three or four in the entire state of Vermont, last time I checked, and at least one was only open in the winter for long-term residents who were there for the entire season. Just something else to consider.

Bigfoot.

What kind of temperatures are you talking about?

You need double pane windows, good insulation, heat to the holding tanks and pipe protection. Staying in cold temps necessitates careful planning and LOTS of propane.

Pulling a trailer on ice/snow should also be considered.

Anything from Northwoods Mfg., Arctic Fox being one of their brands.
and Outdoors RV. i've heard it's owned by Northwoods Mfg. but i'm not sure.
both are mainly only available west of the Mississippi.

they both make true 4 season RVs. they are heavy though.

Montana High Country has been rated zero degrees for about 15 years now. But they take a lot of propane to keep the under belly warm.

There are very few RVs that are suitable for cold weather. Remember its really hard to put much insulation into a 2 inch wall cavity. One of the last true cold rated RVs was Teton. But kost Tetons needed a dually to tow because they were so heavy.

My keystone sprinter fifth wheel has the arctic package

Just be careful of any RV that has as sticker that says "Enclosed Heated Underbelly" but no other "Artic" features. That just means you can use it in April and October.

Outdoors RV
Nash
Arctic Fox

If the wv in your handle indicates West Va, You will find that few are going to do well from the factory.
Most will require you to get creative and help with winterizing, and even then may only be marginal.
Some basics.
Most arctic packages are enclosed under belly and have a small amount of heat being ducted down there from the furnace. Some will have heat pads on the tanks, both methods help but the furnace will be a steady consumer of propane and it can become quite a lot, the tank pads work well if you have 120 VAC all winter.
You can help hold heat with air pillows in the skylight/roof vents to insulate them. Clear plastic added to the inside of windows to ack like a second glass pane helps some too. Some manufacturers offer doule glass or insulated windows which help.
You will need a heat tape on your water supply hose, and will need to find a creative way to insulate the faucet as well as the drain lines.
Bales of straw or some form of skirting to enclose the areas under the trailer will help a lot too.
Drop lights with old school incadescent bulbs or an electric space heater will help under the trailer also after it's skirted.

If you have unlimited electricity avail;able, the temptation will be to use space heaters, but you have limited ability in a 30 or 50 amp trailer to connect stuff. You may find that a small propane space heater will work better.

There are other tips and tricks, most will help some, but the only one that really works well is putting the trailer someplace warm be it way down south, or in a heated garage.