what distance are you focusing on?

You are in the right direction.

Thing is, using a fluid trainer is only as beneficial as you push yourself. At those distances I'd just guess you want to log 110+ miles a week for early base weeks and then start increasing it. On the trainer it's going to feel like it's kicker your ass a little harder then the road, so that's normal.

The days you can get out, defiantly get out for longer rides. However, using a trainer inside can be very beneficial with short INTENSE workouts. Just put a lot of miles on, you will see improvements.

Guys above are correct, this time of year the best thing to do is just put in the long hours. Start doing long rides, even if they are slow, and as the season starts to come up ramp up the speed.
If want to ride a 70.3 then you definately should start puttin in the time, SPIN!!!

This is just what I'm doing, I have a HIM in April I want to be solid for. I'm following a few plans but Dec and Jan are my off months from school so I want to pile it on when I can. I've been averaging 4-6 hrs a week on the bike for the past month or so (on the trainer) and it's not too bad.

I am putting in about 5hrs a week on the trainer right now, but I'm also not running until january and am training for a HIM. I am hoping to do both planned HIM bike legs next year at around 20.5-21.5mph avg based on previous results. FWIW

As to the OP's question...I made significant improvement in my bike speed last season (+~2-2.5mph avg over Oly distance), and I can't really explain how specifically, but I'll tell you what I did:
- Over the winter, I attended spin classes at the gym...yes they are only 45 minutes long and on a bike with a flywheel (lots of inertia to keep legs moving), but they broke up the monotony of trainer rides and they introduced a new level of intensity. My avg HR for those workouts was near 170bpm and my normal HR on the bike was around 130. It also gave me a much better idea of what kind of work I should be doing on the trainer at home. Before, every trainer ride was too low intensity. Spinervals workouts are similar in there format to spin classes, so they should be effective as long as you're really pushing.
- Once it got warm enough to ride outside consistently (I live in OH so I feel your winter pain), I did with basically 2 workout types I'd switch between. 1 where I'd ride a flat and open route (little traffic and stoplights) while focusing on a higher cadence and staying in my aero tuck. I'd do some 2-3 min intensity bursts, where I'd push it pretty good spaced throughout the ride. These rides would generally be about (1-2mph sub race pace). The other workout, I'd just go exploring and find as many legitimate hills (there are plenty here in Cincy) as possible and ride them (in the amt of time I had planned to ride). This was really fun and helped build up my leg strength.
- Also, not related to the bike particularly, but racing in general, once I got into the build phase, I'd run off the bike 1 day per week starting at about 1.5 miles and building to 4 or so. This run was focused on high cadence and really helped me get in my running groove immediately out of T2. I'd do this on my flat aero riding days.

Anyways, that's a lot of specifics, but since I'm not totally sure where the gains came from I figure I'd lay it out there.
I was riding about 75-80 miles/week for my longer weeks (it was an Oly focus year), so obviously I'll up that this year for 70.3s, but the focus will be similar

Just my long .02

I wish I could afford a watt meter! Is there a cheap brand I could pick up for the time being?

Also, what gear should I be in for the workouts you described? After doing those sets should I just go back to a normal cadence for about an hour?

Honestly Donner, keep it simple. You don't need to spend money to be fast (even though it helps).

Just take your bike, and hit the road, everyday, and take scenic routes and enjoy the sport. Make sure you do speed work and stuff ,but clearly just log miles and you will see improvements, as with anything.

It's all a mental game, the harder you can push your body the stronger it will get (in most cases, unless you abuse it).

+1 to TriSooner. That sounds like a recipe for cabin fever to me (though others may feel differently) on an indoor trainer. I would think it would depend on when your Oly and HIM races are going to be - spring, summer, fall?

My personal recipe for cycling is to maintain through the winter via about 3 - 4 hours a week on the trainer. One 1.5 - 2-hour ride where I watch a movie, and two Spinervals sessions or sessions with intervals.

Then in March, I sign up for a 4-week 15 miler time trial series that our local road racing organization puts on. That makes me get out on the road in early March to start ramping up, and putting in a 15-mile time trial a week for a month gets me revved up into cycling again. Time trials are I think a great way for triathletes to focus on their cycling speed.

Then as the weather gets good in late spring/early summer, I start ramping up into longer rides. I don't usually hit 110 miles a week until maybe the last 3 weeks before peak. But then, I'm not much of a high-volume trainer either. Also, because of where I live, every ride is a hill ride. I think that helps keep the volume lower because intensity is higher.

This usually puts me in shape to average around 20mph for a HIM.

Ride Every Day
Seriously Ride Every SINGLE Day
Your rest day includes biking, even if it only is a 30 minute lark on the community use trail going 10-12mph

Do at least 30 minutes a day on the bike. Start off with about 3-4 weeks of this with just easy riding, Then add in one longer ride start off with about an hour for your longer ride, then add 30 minutes a week until it is 3 hrs. Then add in one interval session a week of 60 minutes, then up it to 90 minutes, then add in a second 60-90 minute interval session. If you get this far you are riding 7.5hrs a week. It should also be warm and you can start extanding your long ride to up to 5 hours.

You have a running and swimming background, so let those slough off for a while. Focus on the bike and you can add the run and swimm in as you like, but pay attention to your body.