Integrating an existing off grid system with new grid tied system

[Cam87]

The situation i have is this, this property has historically been completely off grid (solar,wind and generator). This property currently has a shop with living quarters and a house about 300 feet away. All of the off grid components are in the shop and there is currently an under ground line supplying the house from the shop. The eventual plan is to phase out the off grid system as components age out and eventually just use the generator for back up. For the time being the shop with living quarters will stay on the stand alone off grid system. The house on the other hand will be converted to the grid tied system using the previous off grid system as back up. My plan is to intercept the line from the shop to the house and use a Thomson TS 910 NEMA3 ATS to accomplish this. The other issue is that the area can see extreme cold -40 at times during the year. My plan for this is to install an Omega CREX03 din rail mounted heater. Does this seem like the appropriate solution? Thanks in advance