A bloody big
instrument that is allegedly played almost exclusively by rather heavy males.
Not so, not by a long shot.
I, myself, am a tuba player, and happen to be quite skinny. When I was in the Purdue Marching Band, there were around 32 tubists in it. About half of us were quite skinny. Most of the rest were of average size, athletic. Only 5 or 6 of the whole bunch were of the 'traditional' frame for tuba players. Oh, and we had one girl. She was of normal size for a girl, and normal... ah... distribution, as well. She was very sporting about the whole thing.
Just because you're big doesn't mean you can play a big instrument well. In high school, I was the only tuba player in the band for all four years. You learn to play rather unabashedly. When I got to the college band, and had 30 section mates, I was still making myself heard very clearly. I had good tone, as well. Played in the Symphonic Band next semester. Yay for me.
Of course, the look of it is a bit off. And a skinny man with a sousaphone on his shoulder is rather top-heavy, tends to tip over a lot if he's not careful. Take my word on this.
The key to not falling down is to not start falling in the first place. If you start falling down, and you have 35-45 pounds of expensive brass on your shoulder, SAVE THE TUBA. The doctor bills will be much less than getting the dents pounded out. Count on throwing yourself under the damned thing to cushion it's fall.
Along this same vein, it is possible to shine the bell of a sousaphone to a high, mirror-like gloss. It can then be used to see behind you for occasions when your psychotic director wants you to march backwards. This will prevent much tripping over drums, slipping in mud, and damage to the all-important instrument.
A side note: sit-down tubists are more prone to be on the large side compared to marching tubists. The causes here should be fairly obvious.
Playing a tuba in freezing weather is an especially risky behavior. It's not good for any brass instrument, but tubists have it worst because there's more metal to freeze to. I froze to my mouthpiece once, in a competition, and ended up having to get a cup of coffee to thaw the damned thing off of my lips. Horrible experience, wouldn't recommend it.
Tubas are expensive, heavy, and generally have the most boring parts in the score. This is exactly why we are fiercely proud. We are also, apparently, prone to writing sprawling, meandering write-ups. Ah, well, such is life.