Good solution to your power problem. I've used my little 2KW inverter generator to keep us going during outages. It can alternatively run refrigeration, the microwave, lights, computers, and so on. We have a wood stove to make heat. Sadly, we are on a well, and it cannot run the 240 Volt well pump.
Addressing others' concerns.
Depending on your generator, you MIGHT be able to back-feed the main panel - if the generator puts out 240 Volts. This is unlikely with an RV generator, because most are wired for 120 Volts only...even the Onans.
A typical 120 Volt generator could only power half of the main panel, and it would require some expensive connectors to adapt a 30 or 50 amp 120 volt RV circuit to connect to the generator's output. And the "double-male" adapter would be dangerous indeed. While it's technically possible to connect a 20-amp outlet from an RV generator to a portion of the home's circuitry, it's kind of pointless.
You've (the OP) made it clear that you're just feeding 120 volts to individual "appliances" via an extension cord. No risk of back-feeding the grid with this arrangement. If you unplug the fridge from the wall and plug it into an extension cord connected to the generator, that system is totally isolated from the grid. Your "kluge" with the furnace is essentially the same thing.
If power outages are a "thing" in your area, you might consider permanently splicing in a male and female plug/socket in your furnace connection to simplify the changeover. A short #12-3 AWG extension cord can be cannibalized for this purpose. The furnace is probably connected to the panel with #14 wire. Turn off the breaker for the furnace circuit. Install a
single socket in a box on the end of the power wire that feeds the furnace. Don't use a duplex outlet or someone will surely plug something else into the outlet. Mount it securely. Use the extension cord to connect the furnace to the new outlet box.
with solder to make them more durable in the conventional screw-terminal connections used for solid copper wire. Crimp-on spade connectors would work, too, but the crimp is the weak link in the chain. In a basement environment, these crimp-ons will be prone to corrosion.
Shutting of the main breaker is an excellent precaution any time you're running on generator, but if your genny is not applying power to the panel or main house circuitry in any way, there is no risk of back-feeding the grid.
On the other hand, if you have a 240 volt generator, it's possible to energize the entire panel through a range receptacle (50 amps) or dryer receptacle (30 amps). In this case, you either have a transfer switch (legal) or shut off the main breaker (illegal but safe) to prevent the generator from energizing the grid. The beauty of a transfer switch is that it's fool-proof. The generator cannot energize the panel without disconnecting the circuit(s) from the grid. Relying on the main breaker requires you to remember to do it during a crisis.
I had a remote farm back east, and we lost power pretty often. I had a welder in the garage/shop, and it required a 50 amp circuit. I had a generator and made up a cable that connected to the generator's 240 volt output and plugged into the welder outlet. This custom cable had male connectors on both ends, so it was a very dangerous piece of wire. I'd kill the main breaker, plug into the welder outlet, and only then connect to the running generator. Do this out of sequence, and a male plug end could be live with 240 volts and as much as 50 amps. Certain death. This arrangement was adequate to run the well pump, the furnace, basic appliances, and so on with a 5 KW 240 volt generator. I kept my "special" cable secured in a locked cabinet. Without a transfer switch, this was NOT legal, but it worked well and,
with the main breaker off, it was safe.
As for pulling the meter, this is not only unnecessary but it will also get you in trouble with the power company if you break the seal.
Thanks again for sharing your innovative way to use your RV as a power station.