I don't think this is the answer for your situation. The purpose of a Buck Boost Module is to Boost a lower voltage to work with a device that needs a higher voltage at all times.  I don't believe its purpose is to "carry a device during a temporary drop in voltage".  I have used these with microcontrollers where I might have a 12V source but a device needs 24V full time. These are low current situations.

Apparently the Buck Boost converters convert the lower DC voltage to Alternating current. Since this is then AC, a transformer can increase the voltage to a higher level. Then that higher AC voltage is converted back to DC for the range needed.

In your case the voltage is likely dropping below the 12V level that the Enviso requires to avoid dropping out as you start the tractor. Some tractors have very inefficient starters and the voltage about drops to zero while starting.  This isn't much for a problem with many devices but can cause GPS devices etc. to drop out.

I had this problem several years ago with a Trimble GPS system that used Omnistar for correction. I used this mainly for planting. It was desirable that the Omnistar remain "converged" over night so I did not need to wait for it to reconverge in the morning. One way around this was to connect directly to the battery and leave the system ON all the time. This was not always the answer because the starter would sometimes put such a load on the battery that the voltage would drop out and I would need to turn the GPS system back ON after the tractor started and wait for the convergence process to complete.

Here was my solution: I put a small 12V battery in the corner of my cab and ran the wires to the GPS off of it. I left the GPS on all the time. This kept  Omnistar converged as long as I parked in an open area. I put a wire on the positive terminal of the tractor battery connected to a diode and then to the the positive terminal of the small battery The negative terminal of the small battery was connected to the tractor ground.

This meant that the GPS was being run off of the small battery.  The diode allowed the large tractor battery to charge the small battery whenever its voltage was higher. When the starter was engaged, the diode prevented the tractor battery from dropping the voltage in the small battery so the GPS did not drop out. The large battery charged the small battery (there was a slight voltage drop which was OK). 

I think this approach would have a better chance of success for you than a Boost converter. There would be other solutions but the idea is that the "new extra battery" is used to keep the GPS alive while starting the tractor.