the upper arm is completely housed by the crash structure, which is a replaceable item. not cheap, but certainly not what a chassis costs. the lower arm front bushing mount is a bolt in piece on the tub, but I have seen where they didnt give and tweaked the tub, you guessed it, right behind the drivers seat.... It is still likely that you bent the rails, as the seat mechanism isnt exactly industrial grade...
If this is insurance, I HIGHLY suggest you be involved EVERY step of the way thru estimate and repair, because More times than not when the tub is involved, they will try and hammer it back out etc to avoid the replacement/total loss cost. There should be plenty of copies of the tech service notes floating around to get the statement from Lotus that says the tub should be replaced for ANY damage if you have trouble with your insurance company. If it comes down to a fight, and your car is at a local shop, I will be glad to verify this for your insurance company, pm me and let me know whats going on... I have had to get involved a couple of times in the last 3 years on insurance deals like this, where they claimed the tub was fine, but it had stress cracks etc...
Jason