Adding flodlight to HardieSoffit. Best box to use?

[red92s]

I am adding a motion floodlight under the eaves of the house. There is an existing motion floodlight on the front corner of the house; this will be on the side over the driveway. I am just going to add a junction box in the attic and power both from the same switch location.

Biggest problem I'm having is deciding what box to use to hang the new fixture. It's a well-made, heavy-duty RAB Lighting fixture that weighs several pounds. The soffit panels are vented hardieboard. I'd rather not pull down the soffit panel to attach a box to the rafters, as I worry about damaging it in the process.

For aesthetics, I'd prefer to avoid just surface-mounting a box to the rafter on top of the soffit. I'm not sure I trust an "old work" round box with the little wings in the thin hardiesoffit panels. I don't have interior attic access to the mounting location to mount a box from the top side (should be able to fish wires though).

Would something like one of these be appropriate? I think either one would protrude about 1/4" beyond the soffit since they are made to end up flush with 1/2" drywall.
http://www.homedepot.com/p/Titan3-1...n-Box-with-Plastic-Cover-CPB13NM-SM/205383211
http://www.homedepot.com/p/Westingh...model-Ceiling-Fan-Saf-T-Pan-0103600/204845541

 

[Mustang51js]

Old work box will be fine, the lights aren't that heavy. A round box will have 3 clips in it which is plenty

 

[Jim_No_Garage]

While I can't help you on your question I learned that the HardieSoffit product exists - I have to do the soffits on my house and this seems perfect!

Thanks

Jim