When you're on Siege (or Mugen), failure to place a trap will cause the tinker to take damage. So dress up your tinker in high phys armor and have another character handy for rezzes, if necessary.
I have a character on Siege whose only use (other than collecting gifts) is to make trapped boxes, because I really didn't feel like buying yet another soulstone for my main crafter character. She's got 30.0 tinkering and currently only has about 111 hit points with all her gear on (trying to get it higher but I just don't play her that often). I usually have her borrow the main crafter's tinkering talisman to make trapped boxes so there aren't quite so many failures. She rarely dies anymore from the failures once I monkeyed with her suit to push up her hit points. But it is indeed painful on Siege to make trapped boxes at low tinkering skill!