Stripped Bolts on Rear Trailing Arm

[AtoZed]

Hi,
I am in the process of changing out rear shocks and trailing arm bush. In the process of doing it I appear to have stripped 2 of the 3 bolts which attach the trailing arm (aka longitudinal arm in WIS) to the car body. For the moment I have added 2 washers and tightened the bolts down to a decent tightness, but below 70ft-pounds. I think the problem was the "nut" that the bolt goes into has been stripped since it is the 1st part of the bolt which has its threads shaved off. I suspect I'm going to have to tap 2 new holes. I have never attempted this before so I have to go out and buy a tap/die set. Anything a noob should be aware of before doing this? The bolt is 18mm in size, but what size should I buy to replace it with? I guess I'll have to figure out original thread pitch etc. Will this cause a problem?
In doing some google searching, people talk about helicoils. Would this be easier to install?
Thanks for any insight,
Frank

[RMinNJ]

I am so sorry.. I did the rear arms and tried to adhere to the torque specs posted by
platnoff....namely that 66 to 70 ft/lbs was enough for any of the bolts . Luckily they
all went in straight although lifting/pushing the arm up made it difficult.

I know the feeling...despite a torque wrench I stripped the brake caliber of my
wifes car...with the thick bolts and they being brakes I thought more torque was needed.
From past projects suddenly stripping something is my greatest fear when doing
maintenance. I have broken many things.

For the trailing arm one could put a nut possible on the inside of one of the bolts? But
I don't think there is any way to reach in and hold the nut? If this were me I would admit
humble defeat and drive it slowly to my dealer where they are well versed in tapping and
heli-coils (ask me how I know). I would not feel ashamed for attempting it myself due
to the outragous price for the trailing arm job. A flawed design in my
opinion.