Removing polts from unibody

[wsmm]

Not a classic yet, but I have a 2000 Jeep Grnd Cherokee. I have to replace the fuel tnk skid plate, whitch also holds the fuel tank under the car. I'm worried about the bolts either snapping off or the nuts that are welded inside of the unibody u channel breaking loose. I can seem to see any way to get any pentrating oil on the bolts that stick through the nuts inside the channel.. Open to any and all suggestions on how to handle this issue. Also open to ideas if the bolt snaps off or if the nut breaks loose from the weld. Got to love these engineers. I have an electric impact and an air impact that hasw 700 ft/lbs removal force. plan on using one or both on this job unless advised otherwise.
 

[pcrh]

Did a simalar tast on a Ford Explorer. The problem was more to do with the build up of road grime and dirt covering the bolt. Rust was actually a secondary problem.

I found a power bar to be better once you rattled the bolt with the impact. I found if you keep the impact on you will eventually snap the bolt.

So what I did was rattle the bolt with the impact and then use the power bar. If the bolt moved then I would alternate between tighten the bolt, spray lots of liquid wrench in the general vacinity, then use power bar to loosen the bolt until it started to bind, then tightned the bolt, spray liquid wrench, loosen the bolt until starting to tighten, tightened the bolt, spray liquid wrench, etc repeat and do not get impatient. The road grime will bind the bolt to the nut and something will break..
 

[wsmm]

Not coubting what you say, but the channell that contains the weld nuts for these bolts is totaly enclused. So how would road grime get into the channel and onto the bolt where it extends past the nut.
 

[pcrh]

I did not ask or go looking for the access point. I did drill a small hole near the bolt into which I put the spray tube from the liquid wrench to access the inner threads. Then I just worked it as described until I got the bolts off. Long tedious process.