I too don't ride much outside once winter settles in around me but I keep riding indoors. My bike/trainer now are part of my living room and I try to get at least 45 minutes in each day. The past few winters I have gradually worked my way through my gears - not perfect training plan but I felt strong in the spring. I calculated my gear inches and picked an easy gear to work in for a week or two. Once I feel like I'm not pushing myself I bump it up to the next gear (example: I started in my 53" gear and bumped it up to my 57" last week and this week I'm working with the 58" gear) and I slowly work my way through the various combinations. By the early spring I'm pushing some large gears(mashing I know) but it does wonders for my strength. I do not own any training videos so I spend my time on my bike watching music videos (if I'm riding early in the morning), reading a book and yes sometimes I even grade papers while I pedal away the mindless miles. Not sure if this will help you but thought I would toss it out as a suggestion.