filling kick panel & cowl vents

[BIG HEAD]

i filled in my kick panel vents mainly because of rust, but also just wanted to do away with them. because of my application, for mud bogging, i also filled the cowl vent. the part i want alittle help with is how is my heater going to work? i know i will not get the fresh air. that part i dont care about(unless my passanger starts farting). but i do want a little heat and defrost. will those work at all?