I want to get the chassis to body brackets from under the front wings off as they are rusting. These ones:-

The bolts through the chassis are accessible both sides so shouldn't be a problem.
My question is does anyone have any tips for how to access the bolts that go through the body?
(Mine are installed with the bolt heads inside the car and the nuts catching the muck under the wheel arch )
Theres' no sign of them immediately under the carpet and I don't suppose they are captive?
I'm not sure which bits of trim/underlay to attack and and I'd like to do as little damage as possible in the process.
Any advice greatfully received.
Regards
Bill