your brewing description did not mention any hops addidion.
are you using pre-hopped extract?
If not, the lack of hops could be the reason forf the beer going sour.
I just heat up the oven to ~150, turn off the heat, put the mash pot with lid in the oven, close the oven door and wait. I get very little heat loss that way.
I brewed the same kit in December, left it in the primary for 4 weeks and then bottled in early Jan. Now, after a little more than 5 weeks in the bottle it is just starting to taste OK.
So if you wait a bit longer, it will continue to get better.
The yeast are probably still at work and what you are seeing is the CO2 that they ware releasing. You probably need to leave it for a while before you try to bottle it.
My first was a Grain Belt my cousin and I found floating in a lake while fishing. It was fairly warm and tasted like CRAP! - We poured most of it out!
Then a year or so later, I was given a cold Grain Belt after a HOT day of baling hay and it tasted GREAT. I have been a beer drinker ever since!
If you are worried about sediment in the bottling bucket, just leave the bucket tilted slightly during the secondary fermentation (spigot side higher - just use a wooden shim or something under one edge). This will cause most of the sedimentation to collect on the far side of the bucket.
My first brew was also a Munton's kit and it did smell like crap in the fermenter! But after bottle conditioning at room temp for about a month it got to tasting pretty good. Just have patience (and faith!).