Tri shorts... the padding is a joke. I just go into the race knowing that my butt will hurt on the ride. I can suffer for 10-25 miles. That's how I see it.
Otherwise, I only train in proper bike shorts. My butt can only take so much pain in one lifetime.
Good luck on your training! You can do it! Stay focused and you will be ready to race.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"