It would probably be easiest to use a longer bit. You could drill through the outside and the inside separately but it might be difficult to get the holes lined up correctly.

I'm not sure what the use of so many washers are for. I might try using a stack of washers between the inner and outer panels to act as a spacer to keep the panels from bending towards each other but that's in a different place than closer's pic

 

I only used one washer on each bolt. that's all you need. I used a normal size drill bit too, I don't think its all completely necessary that you get a longer one

 

I too used a 4" or 5" long normal drill bit. It easily drilled through both panels. And a heads-up... I think the two lower-front holes are a little trickier than the others. You have to work at getting the bit to drill throught the inside panel because you're not drilling into a flat part of the panel.
And yea... I didn't have to use so many washers. I just used that many so it was easier to get my nuts on the bolts. I guess I should specify the list of lengths I gave will most definatley get you into the interior, and will also not cause any interference with anything inside either.

 

I don't even remember what lengths of bolts I used anymore... and half of them were too long and I cut them anyway... here is a nice little tip I found it easier to have the nut on the outside for the harder to reach areas, I think I have about 3 or 4 nuts laying between the outer quarter panel and the inner metal. I did that with the 2 bolts on the rear, plus its easier to tighten things if they ever get loose

 

Appreciate the tips. I bought about 30 bucks worth of hardware, I hope I dont have to make another trip to the store lol. Right now it's a bear trying to get it lined up by myself. The ratchet straps help. I'm running back and forth between the blazer and this thread to look at pics to make sure I have everything right before I start drilling.

 

lol its really helpful to have a set set of hands

 

I used two straps and hung it from the luggage rack. I got the two front bolts in and snugged up. Then I took the two straps and ran them to the drivers side to help pull the carrier tight against the body panel so I could drill the rest of the holes where they needed to be.

 

looking good...thats almost exactly how i did it.
those straps come in handy.

 

lol I had a buddy hold mine

 

I started on mine today, didn't finish. Hopefully I can finish it up tomorrow. I have to go back to the hardware store and get some shorter bolts. For anyone considering this, I highly recommend recruiting help lol. I have 2 herniated discs in my back and they're letting me know about it right now.