[A/S] Ladders To Work On AS - Size, How Many?

["qtsazmt"]

I am going to need to purchase a ladder(s) in order to work on the 
top of the AS (i.e. caulking, replacing vent, etc.). What size 
ladder do you need in order to safely/easily access the top of an 
AS. Do any of you use a couple of ladders in tandem (scaffold).I 
have a 79/31' trailer. Thanks, AJ.