DIY 50 amp to 20 amp pigtail

[KnowNuthin]

I want to plug my tractors block heater into our 50 amp RV service for the upcoming winter months…

Our panel has 1 - 50 amp and 2 - 20 amp breakers… both 20 services are taken and currently used year round… (chicken heat lamps, water bowl heaters etc.)…

What I’m envisioning is a 50 amp plug with a 3 wire pigtail connected to the common, neutral and one hot leg… leaving the second hot leg vacant…

This would give me 120v 50 amp at the pigtail end… no?

This would be used STRICTLY for a 600 watt engine block heater…

Is this a bad, terrible or workable idea?

[enblethen]

Your 50 amp should be a double pole breaker.
I think it is a bad idea for what you are thinking.
I would suggest getting thin breaker with two 20-amp breakers and installing a new receptacle. Some call breakers, wafer or tandem.