Ball and trunnion to u-joint conversion?

What makes the boot explode? Sounds like pressure builds up inside? Should it be air-tight? I didn't think so.

Jeep Wagoner guys pioneered the sliding yoke retrofit, since some used the same ball & trunion U-joint PN. I have seen some new sliding yoke driveshafts for sale on ebay, but didn't investigate. They look like perhaps a front axle for a FWD, so might not be long enough. They are affordable though (<$200, I recall). BTW, if faced with a different sized rear U-joint, there are adapter U-joints for various paired sizes.

Personally, I have enough B&T rebuild kits (no, not selling) to last my 2 early A's for life.