If you try to wrap your bus in duck tape, the price will climb climb climb. Using tape is going to be a cash in front, cash during and cash after affair. If you start out with a decent quality tape, you are looking upwards of $10.00 a roll (for really good gaffer/aviation quality tape) or more. If you use el-cheapo-walmarto tape, you are going to be redoing and redoing and, well, redoing tape all day long.
Only the really costly tapes will last any decent time under stress like rain, uv, and wind (whether you are driving or storing outside, wind will get you every time.) Thus, repeated removals and reapplications will be in order.
Then there is the day you want to put a cheap $200-300 paintjob on it. You will spend for-ever and ever and ever trying to remove old tape (which becomes crusty and almost permanently bonds to whatever you don't want it bonding to. And then the removal of tape goo. (Easiest way is to soak in gasoline, light on fire, walk away and start over somewhere else).
Soo... if you need to cover your bus, go get some really cheap paint, maybe check out a paint shop for stuff that's leftover or someone didn't buy, suck it up over the color and just go to town.
Now, on the other hand, if you are just trying to cover up the lettering, duck tape works wonders, but it has the same problems over a smaller area. So end removal and cleanup after it gets baked on can be a problem, but it won't kill you like doing a whole bus.
Done duck tape on cars, and on martial arts weapons for over 28 years, so I got a lot of experience with the tape. It goes on easy (on a clean surface) but removal and cleanup are the big negatives.
So, good luck.