My personal 2 cents...take it or leave it!

Heavy Duty Tubes - Sure, why not...better than ultra-lite racers!
Slime - BIG NO!!!! I would not suggest using this stuff in your tires. It can cause more headaches than its worth in many cases, eg. the slime can pool, making your tires rotate unevenly.

My opinion is...fixing a flat on a ride like that is not a huge deal...lots of support vehicles on the road if you need help (at least there was in Philly).

Good luck by the way...our ride was much fun...hope yours is the same!!!