How far are you going? I used to take some purple rim cap into the LFS when it got to 12" around. The best way that I found was to have somebody hold it in their lap by the base with a plastic grocery sack over it to keep the breeze away. I was only going 12-15 minutes, though - it was always a very long 12-15 minutes. It would slime but was always OK.
In water, they would always break up a bunch. Bubble wrap around the bottom perimeter will keep it more upright and protect it a bit. Some of bottom plates would break with the bubble wrap, but I always though that was better than the top. I used to cut 4" strip and do two times around and then secure it with a stainless safety pin rather than tape.
Good luck.