Drill & tap aluminum pan?

I just got an aluminum trans pan but the only fitting is on the bottom for a plug. I want to run a trans temp gauge and was wondering if it'd be okay to just drill and tap the pan for a 1/8 sender, or is a welded bung a must? The pan is pretty thick.

http://static.summitracing.com/global/images/prod/large/SME-1010R.jpg

I`d drill n tap it in a heartbeat if it`s at least a 1/4" thick!---bob