I'd go with a pair of 120W if you roof mount, or you could probably go portable with a 160w and aiming it at the sun a couple of times a day. You need less watts with the portable vs roof mount, because it's pretty much always in alignment with the sun by aiming 3 or 4 x a day, so it's amperage yield will be considerably higher that flat mounted on the roof, it's much more efficient aiming directly at the sun.
Get a good charge controller also that has adjustable input voltage for the bulk charging mode, and set it for 14.8V, that way you'll hopefully charge to 97 to 98 or 99% daily, instead of just 90% State of Charge at 14.4v.
Been there, done that.