Rehabulitating Oldies-Advise?

This afternoon I am going to go get the old horse from my previous posts to bring him to the barn I board at. His vet has given the OK for the move though I am nervous what the stress will do to his already fragile state. The new barn is really close (20 mins away) though I am mostly afraid of how he will take to the change in environment. I will keep everyone updated on his progress but I would love for everyone to pipe in and give me your advise, experiences, and successes on fattening up old horses.
This horse is ancient (30 years or older) though his teeth are in good condition(the ones he still has) and his blood work was fantastic. I am planning on feeding Triple Crown Senior(soaked) and alfalfa pellets(vets orders). What are your experiences with feeding older, or under weight horses?