Yah, Reds and whites should go into different temperature regimes.
Its my guess that this is all too late for Grancru. Hey Grancru, what did you eventually end up doing?
Right now, I have about the same or lesser volumes that Grancru is asking about. I have two 32 gal barrels containing about 25 gal and one 20 gal barrel containing 10 gal, all Marshal Foch. I'm using another makeshift heating system. This time, because my working volume is smaller, I lined up the barrels with space in-between them. I stuck a 32 watt boot drier (no boot attached) in the space between each pair of barrels (e.g., one drier between 1st and 2nd and one drier between 2nd and 3rd barrel). On top of each barrel, I placed an empty water jug to tent the tarp and allow the warm air to fully cover the barrels. Come to think of it, its time for me to get a thread going on what I'm making.
I'm using a remote sensor to monitor temperature. Its meant for monitoring bbq temperatures but it seems to work ok for my needs. The temperature under the tarp is between 75 and 80 F depending on the ambient temp.
In my earlier posting, I described how I handled a (to me) massive harvest that demanded an improvised heating system NOW. My barn is unheated and the ambient temperatures were consistently below 55 F. I had 6-32 gal barrels filled with about 25 gal of various varieties. Whites (chard and pinot gris) were pressed juice and reds (pinot noir and marshal foch) were crushed berries. They all went under a tarp with a portable 1200 watt oil-filled heater and I kept the temperature at around 75 F. Many worries, the chard was fussy, did not want to ferment, but eventually everyone got going and in the end was happy with the results.
Seth, on reading your thread on the wines you made last year, I can tell that I'm probably way casual about my wine-making compared to you. I want to tighten up my system for making wine but right now my focus is on my vineyard. So far, I've liked everything I've made. But then again doesn't every parent feel that their child is above average?
This winter I'll start building infrastructure to improve temperature control so they can be even more above average.