Lifting the boat onto blocks

[cliffpaul2]

I am looking for a good spot to position the blocks when I lift my boat up for trailer work. There are several "steps", or flat spots in the back on the bottom of the boat. Which ones are strong enough (i.e. have support beams underneath them) to hold the weight of the boat? I can't tell by looking from the inside where the supports are except for two that are pretty close to the center line. I want to put the two sets of blocks as far apart as possible. I appreciate your help.