Agreed with going backwards first. Before that, I'd drill a small pilot hole (about 1/8"), just to be sure you are coming out where you want too... ie no fuel, electrical, water lines near by, and accesible for the required depth. Once you get the whole thing drilled out, campher (sp) the hole to relieve stress on the edges of the glass. This will reduce "chips", nd possibility of cracking later.
good luck!
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Walt B
"Debt-Charged"Black '07 H210SS6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.