Still inside the car

Still inside the car, examine the heelboard at its outer edges where the heater ducting is connected to the heater channel; this is one of the most frequently encountered Beetle Bodge areas, and rust here is commonly dealt with by GRP or even body filler and wire mesh! Welded repairs to this area would certainly destroy the belly pan gasket, and so for a proper repair, the body has to come off the car.
Lift the engine lid and examine the seal, then the folded lips for signs of rusting; also examine the air intake grille. The rear panel (valance) is prone to rot, so check for the use of filler and GRP. Check the fit of the engine bay to valance gasket – gaps indicate that a new rear valance has at some time been welded on in the wrong position!
Before jacking the car, clean all of the dirt from the rear body to damper casting mounting points within the rear wheel arches. This is a prime rot spot, so give it a good stabbing with a blunt instrument. If rot is found here, expect to also find it in the rear bumper mounts, the heater channel closing panels and most probably the heater channel/sill assemblies. Be extra careful when feeling for rot around the bumper mounting points, because sharp edges can make a mess of your hand!
Crumpled bumpers obviously indicate collision damage; perhaps less obviously, you should look for distortion of the flitch panels and engine bay/rear inner
wing areas, which can also reveal collision damage. If you find evidence of collision damage then check the fit of the doors carefully, because heavy damage will have dictated that, if the door gaps are to look right, the hinges and in fact the door surround itself have to come in for some heavy-duty bodging.
Moving on to the underside of the car, apply the handbrake, chock the rear wheels and raise the front end of the car with a jack placed under the track control arm pressing, then support the car on axle stands. Examine the frame head. Rot here is very expensive and time-consuming to deal with and, in most cases, will entail a full strip down to a bare chassis before it can properly be dealt with. Any signs of collision damage on the frame head or axle (torsion bar cars) should be taken very seriously because suspension mounting points could have been disturbed. In such cases, it will pay to commission a motor engineer's report if you are still interested in the car.
Turn the wheels from lock to lock so that you can examine the flitch panels (inner wings); rotted flitch panels are not only a very difficult repair but also indicate that there is a strong likelihood that serious (and perhaps camouflaged) rot will be in adjacent panels.
Using a torch for illumination and a blunt instrument to stab with, check as best you can the underside of the luggage compartment/spare wheel
well. Also check the insides of the front wings; if you find an area which appears to be thicker than the rest then it is filler.
Whilst the front of the car is raised check the wheel bearings, brakes and steering (see mechanical examination).
Slacken the rear wheel nuts, transfer the chocks to the front wheels, raise the rear of the car and support it on axle stands, then remove the road wheels. Examine the inner wheelarch area closely, probing for rot and
checking for body filler or GRP, and look for creases in the panels which indicate poorly corrected rear collision damage. Similarly check the outer heelboard and the underside of the decking (internal rear parcel shelf). Check the inside of the valance.