Effective Training Inc. Message Board

I have a two meter long housing with 40 holes holding the cover in place. I am trying to decide how to GD&T the cover and housing so that all of the holes can be fitted with screws. Can I make all 40 holes my secondary datum? (The mounting plane being the primary datum.) If I do this I fear that after I drive my second screw I may not be able to drive the rest. I could hand start all of the screws and then drive them all home.

Option 2 make one hole on each end of the part tight to the screws - a hole and an aligned slot. The hole can be the secondary datum and the slot the tertiary datum. The problem is that this adds tolerance to the oterh mounting holes and requires them to be bigger than desirable.

How would you handle a part like this?