During this time of the year my schedule doesn't permit afternoon / evening trail specific sessions so I have supplemented something similar as
@LoneRider described. Twice per week in the evenings I perform 30-45min of circuits in zone-1/2 immediately followed by a 45+ minute walk under load. I have done this over the past few years and feel that it keeps my overall endurance and outdoor related strength in maintenance from Dec to mid-March.
My current routine uses a 20lb weight vest for the following circuits. 20min of 5x KB swings + single goblet squat / 5x push-up's on 30s ala Q&D/ATC. Then 10-20 min of step-up's w/additional 40lbs / chins rotating on 30s on 30s off. Heavy farmer's walk to finish then leash up the hounds and head out the door.
Those weekly sessions combined with a bi-monthly longer (2-4hrs) trail run / hike / bike does the trick for maintaining enough fitness to be 'off the couch ready' for whatever adventures may arrise.
@pet' I've worked w/Rob Shaul in the past and some of the MTI philosophy still exists in my annual training and programming.