Given that you'll be arriving after most spectators are set for the day, the chance of getting a view has to come into it as well. The bottom of Bray Hill is fantastic and easily accessible but I expect 6-deep by the time the roads close. Does the main grandstand normally sell out? (I haven't been to the TT for a long time, it's less of an issue at the MGP.)

Quarterbridge, the pub at Union Mills and Gorse Lea just before Ballacraine are some other possibilities that spring to mind. Or if you don't mind a trek up the coast road, then there's the Hibernian road to the Gooseneck.

Hillberry's another spot you can get to from outside quite easily, as is the Creg.