use a heating pad?

I just finished setting up my Keezer / fermentation chamber (no fancy cabinet or taps - yet!). I have a Ranco control running a FermWrap on my Better Bottle and a STC 1000 controlling the freezer temp. I'm currently fermenting a summer ale and it did a great job of holding the temp at 68° during the active fermentation.

Now the fermentation is slowed down and I'm gradually ratcheting up the temp a bit to finish out the beer. However, I find that I have had to raise my freezer temp to get the FermWrap to bring the temp up (going to top out at 71°). Currently the freezer temp is at 9°C (48° F) which is higher than I'd like to keep it when there are full kegs in there. I'm a bit disappointing in the FermWraps ability to raise the temp up in these conditions but maybe that wasn't what it was designed to do.

So I was thinking of just buying an inexpensive heating pad and setting that under the BB and plugged into the Ranco along with the FermWrap. There is some condensation on the walls inside the freezer but nothing on the floor so it seems like that would be OK. Anybody done this? Any better ideas of raising the temp without warming the freezer temp anymore?

Wait, you are using a heat belt to warm a bottle inside a power cooled chamber?
And you want to keep the air temp A but have the beer temp >A

That just seems counter productive to me.

I currently have my ferm fridges set with 2-stage controllers and it basically works like so
I set the temp for "50*"
If the probe is <"49*" plug 1 activates (which is a heating pad attached to the back wall)
if the probe is >"51*" plug 2 activates (which is the fridge itself)

Plug 1 should never be on while plug 2 is active as the probe temp should never be both above 51 and below 49.

That make sense?

Yes, pretty much what you are saying is what I have. My "ferm chamber" will also be the place where my kegs are stored/served from. Right now it only has a hand full of bottled beers in there but I intend to have a couple kegs going soon (the fermenting summer ale will be ready to keg in a week or so). That means I want/need to keep it at serving temperatures.

Yes, I'm sure this is less productive than a dedicated fermentation chamber like you have but since I only brew a half dozen times a year or so I don't see it putting much of a spike into my electric bill.