Looks awesome! Is this one of those eBay ballasts? Mine run hot too. So does the identical 100W MV HX ballast I got from eBay that I put in my R37. The R37's ballast runs so hot that the fixture can be too hot to touch after a few hours. Never had that happen with a 100W ballast before! Granted the thing is very undersized though. OEM 100W MV ballasts are almost twice the size of the puny Advance I put in it.

Thanks! I got it off eBay but I think a different seller since mine was NOS. I was surprised at how hot this ran for a 50w ballast. When I had it in a fully enclosed case, it reached 210F after a couple hours. The current case is a lot better, it only reaches 140F after a few hours. I thought the 100w Advances would have ran cooler than that though. I guess maybe the CWA versions ran cooler. Anyway the 70w PSMH ballast I use in my R47 stays fairly cool running a 100w MV for a few hours.

Wow you could use it to boil water. (well, not the naked ballast of course lol). Yeah I was surprised how hot the Advance ballasts run but they're very small, skimpy ballasts (to fit in compact fixtures I'd imagine, and to cut cost down) so there's poor heatsinking. My 50W MV homemade high bay light is very oversized so the ballast doesn't overheat (but runs inherently hot) and the lamp runs nice and cool too. I actually could fit 100W MV gear and a full size mogul 100W MV lamp in the homemade high bay if I wanted to. Would give off a little more light than the measly ~1500L I get from the 50W MV.

Nice!
I'd love to find a weatherproof metal box for the 50w MV ballast I have.
Had planned to use it for a light in the yard, but never found a box or did anything with it.

Yeah it got quite hot in a completely sealed enclosure. I thought about using a larger box for mine but I wanted something compact so I went with the vented PSU box I had. Interesting that you could fit a 100w MV ballast and full sized lamp in your highbay too.