Bonded panel repairs - opinions please!

Dave, I knew I could rely on you not to mince your words!
I don't think I explained it properly (reading it back it does look dodgy as f8ck!) - I'd grind and trim back the rusty bits to clean metal, use kurust and then etch prime, so no different to a "proper" repair. If it was something more substantial I'd cut the sill out entirely and let in the whole repair panel or just weld smaller patches if there aren't too many of them to grind down afterwards. The bonding question was more to avoid the use of the welder on paper thin Ford tin.
My thinking is that doing it this way will actually result in a stronger repair - as you say, Lotus use bonded sections and they're phenomenally strong - the metal gives way before the adhesive.

Bonded panels in vehicle production has now been in the market for a few decades and with the advancement of bonding technology is becoming a wider used process especially on premium brands where alloy is now used to form bodyshells along with the outer panels.

When vehicles are built they go through a long research process, are then prototyped and a number of models are built pre production in order to analyse not only that the process of production is correct but that the vehicle performs has it should along with an intensive testing schedule of how the vehicle performs in all the environments & conditions that it will operate in - part of that testing is destructive - physically - such as impact testing to ensure that the vehicles structure protects the occupants - along with many other things vehicles are built to absorb energy when involved in an impact collision with panels deforming in order to absorb the impacts energy in a calculated process - how panels are fixed / welded to a bodyshell are all taken into account when this research is undertaken. This is one of the reasons why for the last 15 / 20 years cars have been built from lighter / thinner materials - there is significant impact protection within the bodyshell that all forms the integral construction with welds / fastenings put at critical points so that if impact in that area occurs the energy is absorbed by the vehicle and the risk mitigated to the occupants.

So by bonding the panel instead of it being welded ? neat idea but what you are doing is changing the structure of the vehicle and how it would act if impacted in that area - the sill would normally deform / split at weld points and absorb the energy has designed but with a bonded panel it will deform and continue to transfer the impact energy into the vehicle rather than splitting on weld points - it's an important factor - likewise when owners think that they are making a better job than that of when the vehicle was first manufactured by putting additional welds in place when replacing panels.

It may all appear unimportant but when you have seen vehicles physically impact tested - inspected them both before & after the impact you can begin to understand why vehicles are built like there are today - it's up to you should you take the risk - what's the chance of someone being in the wrong place at the wrong time with a wrongly fitted structural panel to the vehicle ??

If it's got to the stage of where the sills need work there's a good chance the inner panel around the fuel filler neck is cabbaged as well and the rear inner 1/4 which both come into the prescribed areas for seat belt mounts . Front chassis rails inner wings around the subframe mounts too . I've seen some really neat bodging with seam sealer . The only ones I see that aren't rot boxes are very late 06 07 cars the earlier ones are patched up and on borrowed time now

Is the car worth trying to save? I don't know, I've not seen it yet! Knowing the owner I suspect that the rest of it is pretty tidy, she's not the sort to drive an absolute sh1tter!
Froggy and Stevo, I know what you mean about there being more rot hidden, so I will make it clear to the owner that if it looks worse on initial inspection it might be time to bite the bullet and replace the car.
GN, thank you for your reply, makes perfect sense!

Bonding is wide spread across certain makes of vehicles BMW for instance method of repair is bond and rivet, not conventional pop rivets i might add

modern repair method on a BMW

KA panels are no thinner than most moderns, I have patched a few, you need to go careful on butt joints and get it clean first but it is not that difficult.

bonding could be fine but the only proven route is like for like as the MOT requirements prescribe.