I've been searching the web for info on training for a double century and have found lots - in fact probably too much. Does anyone have any site that they recommend?

I've been riding since last spring and have worked really hard for the past 7 months to increase my speed and endurance. Riding with my hubby really challenged me I think. Next spring he and his brother are riding a 300km+ ride from Banff to Jasper. It has some climbing (5600' total gain) and weather challenges (can be cold, unpredictable, and even snow in June). I want to try to do the ride and think I'll need to train in some organized fashion if I want to even try to be able to keep with them.

Any suggestions as to which training plan works well?

Thanks,
barb