Nowadays I like to use indian head gasket shellac with the paper gasket for this job. It is tackier than RTV right out of the bottle, which makes it easier to keep everything lined up. Cleans up right away with acetone, no scraping or scrubbing.
I put a little bit around the inside of the lip on the Tstat, and set it in place. I'm pretty sure I always orient it so that the "bar" on the face is horizontal (and so that the hole I drilled in the flange is at 12 o'clock). Paint both sides of the paper gasket with the shellac and let that sit for 15 minutes or so. Stick it to the cleaned surface of the housing using the two mounting bolts to line it up. Place the housing, gasket, and bolts into position as an assembly, then fiddle with getting the bolts started, and snug them down.
Do you have much pitting on the gasket surfaces on the housing or the head? The aluminum-iron interaction can cause pitting- in my case the iron head has taken the worst of it. Still never had trouble with it leaking, but I doubt I could get by without using a gasket like some people do. I've thought about filling the pits with JB Weld, but won't bother until I can't get it to seal anymore.
If you use RTV, make sure you let it set-up (skim over) before installing the housing, and then only snug the bolts to finger tight. Let that sit about an hour and then snug the bolts up the rest of the way. You want to let it harden some before clamping down on it, else you will squeeze all of it out.
Also, as with most gaskets, tighten the bolts incrementally. Don't torque one all the way down and then do the other.