is it possible to enclose a generator with the muffler left inside and if so how would i construct the enclosure to get the proper ventelation would leaving the bottom open and a fan be enough.thanks in advance
A portable generator produces a lot of very poisonous carbon monoxide, not to mention fire-hazard heat, and I would not enclose it if it were me.
Mine sits year-round on a covered. but open, side porch and I keep the windows and doors tightly closed on that side when using it.
If you just want a secure place to store it as well as use it, I would build a small shelter with a metal frame, metal roof and chainlink "walls" and locked gate.
Can't terminate the exhaust inside of an building/structure.
While the hot exhaust will be lighter then air. It won't all go outside through your openings. The exhaust will need to be extended out of the building. And then an air intake vent installed. Sized at about 300 sq in for every gallon of oil, or gasoline the generator uses an hour.