You can use the Malfunction & Repair charts. There is a good guideline for when to roll for a malfunction on page 70 of Vehicle Manual.
Once you get malfunction,use the chart on p72 to determie the malfunction. The Construction & Design tables on pp68-69 can b usedto determine length of repair.
If you want to get a standard upkeep amount, I would recommend some amount like 1% or less of the ship value per month in use, not counting Malfunctions and battle damage (and accidents).
