My preferred winter/can't find a pilot trainer is the Wahoo Kicker, but it doesn't support the 145mm dropout (it is a wheel off design so no tire wear). Prefer it over the Computrainer simply because it is blind accessible, but I can also download GPX files to ride or program my own sessions.

Have you checked into a local spinning class? Usually a little more motivating than grinding away in the typical trainer [social aspect], usually about an hour a couple times a week [but intended to be higher intensity than your normal 3-4 hour ride].

San Diego? Isn't Mt Baldy close? And they do blow snow at that ski hill in the San Bernadino National Forest [the turn off to the hill is off I15 before you get to the top of Cajone Pass/Victorville]. Snowshoeing uphill works a lot of the same cycling muscles.

As for the tandem in a trainer... Even if it is "tandem rated," that's a lot of lever on a small connecting point; you have t be smooth, make sure your QR [if you are so equipped] is suitable for the trainer your using, and I personally wouldn't stand [again you have to be really smooth... LOOONG lever]. And for the price of one of those fancy CompuTrainer/Wahoo KICKR things you could easily pick up a couple of CraigsList bikes and single trainers and a few inspirational DVDs/CDs.

Rear tire wear- I always save those tires I no longer feel comfortable running on the road and "run them 'til the explode" on my fluid resistance trainer... I find great satisfaction in these blowouts and a generally positive feeling in knowing I got the very last inch of rotation out of a tire carcass.

My $0.03
[Hey, I'm saving for my dream build ]