Its a shame theres no one to take your snake while your away.
What type of bus are you going on? Is it a coach? Cos they tend to be warmer. Temperature is going to be your main issue, i'd say rather than stress.
Do the coach company your travelling with take animals on board? or are you not going to tell them? If they don't take them then i wouldn't tell them lol.
Once your on the coach it should be alright, how are you getting to the coach are you getting a lift? ie. not walking? just cos its so cold here this time of year.
Once you have your snake with you on the bus then i'd say to put him in a small sack, a pillow case works well for bigger snakes, i used to use a little cotton sack that some pillows i bought came in, when my snake was as small as yours. If you put him in the sack, then in your little plastic tank then he should be ok, the stress levels will be reduced if he remains in darkness the whole time. Plus if it gets cold on the bus you can use the sack to transfer your snake to your pocket so it can get some body warmth.
Thats probably what i'd do if i was in your position, hope that helps
All the best
Tom