1: Chest vaults are OP. Here are comparable cost and breaktimes:

Base breaktimes:

*The total time to break a block is always a multiple of 1⁄20 of a second, or 1 game tick, any remainder is rounded up to the next tick.

Block - basebreak in seconds [optimalbreak in seconds]

Obsidian - 9.4 [1.81] {37 ticks}

DRO = 66600 ticks

IRO = 9250 ticks

Iron door - 0.65 [0.125] {3 ticks}

(15x easier than Obby | 13 easier because of tick rounding)

Wooden door - 0.4 [0.077] {2 ticks}

(24x easier than Obby | 19 easier because of tick rounding!)

Chest - 0.35 [0.068] {2 ticks}

(27x easier than Obby | 19 easier because of tick rounding!)

1 Layer DRO bunker with doors protecting a double DRC

Cost: 118 DRO - 13 DRID - 2DRC

Total cost: 133d

Total breaktime: 73800 ticks

Picture: http://i.imgur.com/2KruDZ9.png

133 single chest vault

Total cost: 133d

Total breaktime: 239400 ticks to break half of the chests. That is 3x better protection!

Comparison of vault costs without doors [cost and then tick break time]

1 layer: 5d 69600

2 layer: 19d 135600

3 layer: 44d 201600

4 layer: 85d 267600

5 layer: 146d 333600

Chest vaults:

5 chests 18000

19 chests 68400

44 chests 158400

85 chests 306000

146 chests 525600

2: Next, mind your corners. Make sure to top off the top corners of any obsidian structures that you don't want people glitching into!

BAD: http://i.imgur.com/YDwQ44x.png

GOOD: http://i.imgur.com/jU7CwXH.png

3: Bastions Chest vault = best.