We have an Addco cover for our 29' TT. I lean an extension ladder against the side with a folded up blanket or something behind it to protect the edge of the roof. The ladder needs to be extended above the edge of the roof a couple of feet. Then I joist hoist the whole cover in it's bag on a shoulder, climb up and toss it onto the roof. We roll it up so that I can start at the rear of the roof and roll it towards the front. I push the sides over as I roll it out forward. Then I go down the ladder and tug it down all around until it hangs right. Usually takes around 30 minutes to get it up and all rolled out.
This is my method and others will have their own versions. The Addco covers aren't very heavy. I'd sure hate to have to climb a vertical RV ladder with a cover. If you look up specs on your make & model, it should say if it's a walk-able roof. Ours does at least.
