Don't give up yet[8D], here is my 1 cent:
The main problem of running in snow IS THE CLEARANCE.
That is why jeep has high clearance. Snowmobile has low clearance but its track is actually its bottom, so it has 'movable clearance'. The blizzard toy car has moderately high clearance only, but it has tracks different from our model tank by having numerous perforations to act as claws instead of track.!
Pads & high speed will work only if 1) it has streamlined flat bottom 2) it is light weight ( snowmobiles) to glide above the deep snow.
Highly perforated CLAW tracks will work if 1) streamlined flat bottom 2) extreme High torque.
Since a model tank's tracks, gear box, & bottom shape cannot be COMPLETELY modified to that extent, you are at least left with MODIFYING THE CLEARANCE : by raising the SUSPENSION, with adding a few extra track links.
It requires quite a bit of work, but it will not ruin its look in snow-runs, & in summer you can revert it back to normal height.
HOPE THIS WILL HELP.
" In science & technology, nothing is impossible. It just need enough determination " I always said. Pierre