So on really cold days if we run a lot of water shower/laundry we get a really bad smell in basement of septic gases. So I am thinking the vent line is freezing. What is the best solution for this, my plumber thinks I should put in a house trap. Is there any other simpler solutions?

Increase the size of the vent(s) thru the roof, if you're sure they are freezing over. I would not go with a house trap.

"...Increase the size of the vent(s) thru the roof, if you're sure they are freezing over. I would not go with a house trap...."

And insulate the vent plumbing in the attic up to the underside of the roof.

if the roof vent is freezing, i would think you will get gurgling when a fixture drains.
just like opening a 2 liter bottle of pepsi and turning it upsidedown.

So it never makes gurgling noise do you think it could be something else besides a frozen vent pipe, i just assume that is the problem since this only happens on really cold days, like 4 times a year

that is strange.. as i said, when a vent is blocked (especially a main vent) there is no "free flow of air" in the piping and gurgling is 99.9% guaranteed.
plus, if the vent thru the roof is frozen solid, it will not just thaw out in one day unless heat is applied to it.
once again, if the vent is blocked and you flush a toilet, as that water is flowing down the drain, it pushes air ahead of it and it pulls air from behind it. no vent or severely restricted vent and the result will be gurgling.

strange is my life...but thanks for your feeback and info



Edited 1 times.

"""Just a vague idea, During extremely Cold days, does your room heating increase or run throught the day, if yes then chances are that due to heat the bacteria in sewage may be multiplying rapidly thus generating odour. Does ur waste line opens up in the sump or is directly connected to the sump station?
"""