Safe way to heat tent cot?

I have this Kamprite double tent cot and want to know if there are any safe tent heaters I can use inside. Would battery operated be better? I’m guessing anything electrical, used with a power generator, would be too noisy and indiscreet?

I have this Kamprite double tent cot and want to know if there are any safe tent heaters I can use inside. Would battery operated be better? I’m guessing anything electrical, used with a power generator, would be too noisy and indiscreet?