Been there, done that, no major damage.
Fortunately, the plumbing is generally somewhat flexible plastic.
Perhaps starting the [b]water heater, and just leaving it on pilot for a while, would be a good idea make draining it a less futile experience.
bulbs as heaters are great for milder climates. At todays high of -6 deg C, I think that only light
bulb which will help the components under the trailer would be a [b]heat lamp, but that might be a good idea.
I definitely think that opening cabinet doors as Charlie suggested is a good idea, necessary if you expect to [b]thaw by heating the interior. I don't know if this is the Rear Gaucho (RGH) or Side Gaucho (RGH) plan, but in the B1700RGH the water lines run between the curbside kitchen and streetside bath/service areas on top of the (uninsulated) floor, through the "hamper" and under-gaucho cabinets. With the doors closed, they're probably closer to the outside temperature than the inside temperature! Air will not circulate down in the hamper cabinets well, because they are only open on top. The pump and drain valves are on the floor under the gaucho - an electric space heater in there might be a good plan.
To get [b]antifreeze into the system with everything under the floor already frosty, the intake hose could be pulled off of the pump and a temporary hose stuck in the antifreeze jug.
Finally, for those of us who don't own a garage which will fit a trailer over 7 feet tall, there is
an option for doing this inside:
Address : 6025 104 Street NW, Edmonton, AB T6H 2K6
Telephone : 780-437-7386
These guys rent space by the hour or by the day. You could haul the trailer in there, leave it to thaw, winterize it in there, then take it home. It sounds expensive, but use of the shop complete with tools is only a few dollars an hour; longer term use is cheap enough that people put vehicles in there for weeks for complete bodywork projects.
If you need to dump tanks afterward, you could go straight to a free public dump location such as the Flying J truck stop on the north side of Sherwood Park:
Flying J Travel Plaza
10-50 Pembina Road
Sherwood Park, AB T8H 2G9, Canada
And welcome to FiberglassRV!