Mike,
The weather-strip material is available from BCS (Beaver Coach Sales) by the foot. Measure the exact length you need, add a foot to be on the safe side, and they will cut the material and ship the material to you. The rivets are available from the local Ace hardware. Just drill the rivets, remove the metal retainer, and old weather-strip. Installation is just the reverse procedure except you will need to cut the weather-strip to the exact length after it is partially installed.
Installing the lower slide weather-strip does not require a skinny professional. The average handyman in reasonable conditional can do it if you stretch above the basement compartments or remove one of them. At 5' 11" and 200 lbs., I had no problem in replacing the weather-strip on my coach.
Gerald